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<!DOCTYPE html>
<html class="split chapter"><head><meta charset="utf-8"><title>10 Executable Code and Execution Contexts # Ⓣ Ⓔ ① Ⓐ — Annotated ES5</title><link rel="stylesheet" href="style.css"><link href="x9.html" title="9 Type Conversion and Testing " rel="prev">
<link href="spec.html" title="TOC" rel="index">
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</head><body><div class="head">
<h2 id="top">Annotated ECMAScript 5.1 <span id="timestamp"></span></h2>
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<a href="x9.html">← 9 Type Conversion and Testing </a> –
<a href="spec.html" class="toc-nav">TOC</a> –
<a href="x11.html">11 Expressions →</a>
<ol class="toc"><li><a href="x10.html#x10" id="x10-toc">10 Executable Code and Execution Contexts</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.1" id="x10.1-toc">10.1 Types of Executable Code</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.1.1" id="x10.1.1-toc">10.1.1 Strict Mode Code</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.2" id="x10.2-toc">10.2 Lexical Environments</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.2.1" id="x10.2.1-toc">10.2.1 Environment Records</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.2.1.1" id="x10.2.1.1-toc">10.2.1.1 Declarative Environment Records</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.2.1.1.1" id="x10.2.1.1.1-toc">10.2.1.1.1 HasBinding(N)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.2" id="x10.2.1.1.2-toc">10.2.1.1.2 CreateMutableBinding (N, D)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.3" id="x10.2.1.1.3-toc">10.2.1.1.3 SetMutableBinding (N,V,S)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.4" id="x10.2.1.1.4-toc">10.2.1.1.4 GetBindingValue(N,S)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.5" id="x10.2.1.1.5-toc">10.2.1.1.5 DeleteBinding (N)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.6" id="x10.2.1.1.6-toc">10.2.1.1.6 ImplicitThisValue()</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.7" id="x10.2.1.1.7-toc">10.2.1.1.7 CreateImmutableBinding (N)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.1.8" id="x10.2.1.1.8-toc">10.2.1.1.8 InitializeImmutableBinding (N,V)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.2.1.2" id="x10.2.1.2-toc">10.2.1.2 Object Environment Records</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.2.1.2.1" id="x10.2.1.2.1-toc">10.2.1.2.1 HasBinding(N)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.2.2" id="x10.2.1.2.2-toc">10.2.1.2.2 CreateMutableBinding (N, D)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.2.3" id="x10.2.1.2.3-toc">10.2.1.2.3 SetMutableBinding (N,V,S)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.2.4" id="x10.2.1.2.4-toc">10.2.1.2.4 GetBindingValue(N,S)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.2.5" id="x10.2.1.2.5-toc">10.2.1.2.5 DeleteBinding (N)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.1.2.6" id="x10.2.1.2.6-toc">10.2.1.2.6 ImplicitThisValue()</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li></ol></li><li><a href="x10.html#x10.2.2" id="x10.2.2-toc">10.2.2 Lexical Environment Operations</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.2.2.1" id="x10.2.2.1-toc">10.2.2.1 GetIdentifierReference (lex, name, strict)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.2.2" id="x10.2.2.2-toc">10.2.2.2 NewDeclarativeEnvironment (E)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.2.2.3" id="x10.2.2.3-toc">10.2.2.3 NewObjectEnvironment (O, E)</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.2.3" id="x10.2.3-toc">10.2.3 The Global Environment</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.3" id="x10.3-toc">10.3 Execution Contexts</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.3.1" id="x10.3.1-toc">10.3.1 Identifier Resolution</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.4" id="x10.4-toc">10.4 Establishing an Execution Context</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.4.1" id="x10.4.1-toc">10.4.1 Entering Global Code</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.4.1.1" id="x10.4.1.1-toc">10.4.1.1 Initial Global Execution Context</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.4.2" id="x10.4.2-toc">10.4.2 Entering Eval Code</a>
<b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> <ol><li><a href="x10.html#x10.4.2.1" id="x10.4.2.1-toc">10.4.2.1 Strict Mode Restrictions</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.4.3" id="x10.4.3-toc">10.4.3 Entering Function Code</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li><li><a href="x10.html#x10.5" id="x10.5-toc">10.5 Declaration Binding Instantiation</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li><li><a href="x10.html#x10.6" id="x10.6-toc">10.6 Arguments Object</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b> </li></ol></li></ol></nav>
<h2 id="x10">10 Executable Code and Execution Contexts <a href="#x10">#</a> <a href="#x10-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h2>
<h3 id="x10.1">10.1 Types of Executable Code <a href="#x10.1">#</a> <a href="#x10.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h3>
<p>
There
are three types of ECMAScript executable code:</p>
<ul><li><p><dfn id="global-code"><i>Global code</i></dfn> is source text that
is treated as an ECMAScript <i><a href="x14.html#x14">Program</a></i>.
The global code of a particular <i><a href="x14.html#x14">Program</a></i>
does not include any source text that is parsed as part of a
<i><a href="x13.html#x13">FunctionBody</a></i>.</p>
</li>
<li><p><dfn id="eval-code"><i>Eval code</i></dfn> is the source text
supplied to the built-in <code><b><a href="x15.1.html#x15.1.2.1">eval</a></b></code> function. More precisely, if the parameter to the built-in <code><b><a href="x15.1.html#x15.1.2.1">eval</a></b></code> function is a String, it is treated as an ECMAScript <i><a href="x14.html#x14">Program</a></i>.
The eval code for a particular invocation of <code><b>eval</b></code>
is the <a href="#global-code">global code</a> portion of that <i><a href="x14.html#x14">Program</a></i>.</p>
</li>
<li><p><dfn id="function-code"><i>Function code</i></dfn> is source text that
is parsed as part of a <i><a href="x13.html#x13">FunctionBody</a></i>.
The <i>function code</i>
of a particular <i><a href="x13.html#x13">FunctionBody</a></i>
does not include any source text that is parsed as part of a nested
<i><a href="x13.html#x13">FunctionBody</a></i>. <i>Function
code</i> also denotes the
source text supplied when <a href="x15.3.html#x15.3.2" class="term-ref">using the built-in <code><b>Function</b></code> object as a constructor</a>. More precisely, the last parameter
provided to the <code><b>Function</b></code>
constructor is converted to a String and treated as the
<i><a href="x13.html#x13">FunctionBody</a></i>. If more
than one parameter is provided to the <code><b>Function</b></code>
constructor, all parameters except the last one are converted to
Strings and concatenated together, separated by commas. The
resulting String is interpreted as the <i>FormalParameterList</i>
for the <i><a href="x13.html#x13">FunctionBody</a></i>
defined by the last parameter. The function code for a particular
instantiation of a <code><b>Function</b></code>
does not include any source text that is parsed as part of a nested
<i><a href="x13.html#x13">FunctionBody</a></i>.</p>
</li></ul><h4 id="x10.1.1">10.1.1 Strict Mode Code <a href="#x10.1.1">#</a> <a href="#x10.1.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
An
ECMAScript <i><a href="x14.html#x14">Program</a></i>
syntactic unit may be processed using either unrestricted or strict
mode syntax and semantics. When processed using strict mode the
three types of ECMAScript code are referred to as strict global
code, strict eval code, and strict function code. Code is
interpreted as <a href="#x10.1.1" class="term-ref">strict mode code</a> in the following situations:</p>
<ul><li><p>
<a href="#global-code">Global code</a> is strict global code if it begins with a Directive Prologue
that contains a Use Strict Directive (see <a href="x14.html#x14.1">14.1</a>).</p>
</li>
<li><p>
<a href="#eval-code">Eval code</a> is strict eval code if it begins with a Directive Prologue
that contains a Use Strict Directive or if the call to eval is a
direct call (see <a href="x15.1.html#x15.1.2.1.1">15.1.2.1.1</a>) to the <a href="x15.1.html#x15.1.2.1">eval function</a> that is contained
in <a href="#x10.1.1" class="term-ref">strict mode code</a>.
</p>
</li>
<li><p>
<a href="#function-code">Function code</a> that is part of a <i><a href="x13.html#x13">FunctionDeclaration</a></i>,
<i><a href="x13.html#x13">FunctionExpression</a></i>,
or accessor <i>PropertyAssignment</i>
is strict function code if its <i><a href="x13.html#x13">FunctionDeclaration</a></i>,
<i><a href="x13.html#x13">FunctionExpression</a></i>,
or <i>PropertyAssignment</i>
is contained in <a href="#x10.1.1" class="term-ref">strict mode code</a> or if the function code begins
with a Directive Prologue that contains a Use Strict Directive.</p>
</li>
<li><p>
<a href="#function-code">Function code</a> that is supplied as the last argument to the built-in Function
constructor is strict function code if the last argument is a
String that when processed as a <i><a href="x13.html#x13">FunctionBody</a></i>
begins with a Directive Prologue that contains a Use Strict
Directive.</p>
</li></ul><h3 id="x10.2">10.2 Lexical Environments <a href="#x10.2">#</a> <a href="#x10.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h3>
<p>
A
<i>Lexical Environment</i> is a <a href="x8.html#specification-type">specification type</a> used to define
the association of <i>Identifiers</i>
to specific variables and functions based upon the lexical nesting
structure of ECMAScript code. A Lexical Environment consists of an
<a href="#x10.2.1">Environment Record</a> and a possibly null reference to an <i>outer</i>
Lexical Environment. Usually a Lexical Environment is associated
with some specific syntactic structure of ECMAScript code such as a
<i><a href="x13.html#x13">FunctionDeclaration</a></i>,
a <i>WithStatement</i>,
or a <i>Catch </i>clause
of a <i>TryStatement</i>
and a new Lexical Environment is created each time such code is
evaluated.</p>
<p>
An
<a href="#x10.2.1"><i>Environment Record</i></a> records the identifier bindings that are
created within the scope of its associated Lexical Environment.</p>
<p>
The
<dfn id="outer-environment-reference">outer environment reference</dfn> is used to model the logical nesting of
Lexical Environment values. The outer reference of a (inner) Lexical
Environment is a reference to the Lexical Environment that logically
surrounds the inner Lexical Environment. An outer Lexical
Environment may, of course, have its own outer Lexical Environment.
A Lexical Environment may serve as the outer environment for
multiple inner Lexical Environments. For example, if a
<i><a href="x13.html#x13">FunctionDeclaration</a></i>
contains two nested <i>FunctionDeclarations</i>
then the Lexical Environments of each of the nested functions will
have as their outer Lexical Environment the Lexical Environment of
the current execution of the surrounding function.</p>
<p>
Lexical
Environments and Environment Record values are purely specification
mechanisms and need not correspond to any specific artefact of an
ECMAScript implementation. It is impossible for an ECMAScript
program to directly access or manipulate such values.</p>
<h4 id="x10.2.1">10.2.1 Environment Records <a href="#x10.2.1">#</a> <a href="#x10.2.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
There
are two kinds of Environment Record values used in this
specification: <i>declarative environment records</i> and <i>object
environment records</i>. <dfn id="declarative-environment-record">Declarative environment records</dfn> are used
to define the effect of ECMAScript language syntactic elements such
as <i>FunctionDeclarations</i>,
<i>VariableDeclarations</i>,
and <i>Catch</i> clauses
that directly associate <b>identifier</b> bindings with ECMAScript
language values. <dfn id="object-environment-record">Object environment records</dfn> are used to define the
effect of ECMAScript elements such as <i><a href="x14.html#x14">Program</a></i>
and <i>WithStatement</i>
that associate <b>identifier</b> bindings with the properties of
some object.</p>
<p>
For
specification purposes Environment Record values can be thought of
as existing in a simple object-oriented hierarchy where Environment
Record is an abstract class with two concrete subclasses,
declarative environment record
and object environment record. The
abstract class includes the abstract specification methods defined
in Table 17. These abstract methods have distinct concrete
algorithms for each of the concrete subclasses.
</p>
<center>
<table width="690" border="1" bordercolor="#000000" cellpadding="8" cellspacing="0" rules="ROWS"><caption>Table 17 — Abstract Methods of Environment Records</caption>
<colgroup><col width="211"><col width="445"></colgroup><tbody><tr valign="TOP"><td width="211" height="11" bgcolor="#c0c0c0">
<p>
<i><b><span class="table-header">Method</span></b></i></p>
</td>
<td width="445" bgcolor="#c0c0c0">
<p>
<i><b><span class="table-header">Purpose</span></b></i></p>
</td>
</tr><tr valign="TOP"><td width="211">
<p>
HasBinding(N)</p>
</td>
<td width="445">
<p>
Determine
if an environment record has a binding for an identifier. Return
<b>true</b> if it
does and <b>false</b>
if it does not. The String value <i>N</i>
is the text of the identifier.</p>
</td>
</tr><tr valign="TOP"><td width="211" height="43">
<p>
CreateMutableBinding(N,
D)</p>
</td>
<td width="445">
<p>
Create
a new mutable binding in an environment record. The String value
<i>N</i> is the text
of the bound name. If the optional Boolean argument <i>D</i>
is <b>true</b> the binding is may be subsequently deleted.
</p>
</td>
</tr><tr valign="TOP"><td width="211" height="76">
<p>
SetMutableBinding(N,V,
S)</p>
</td>
<td width="445">
<p>
Set
the value of an already existing mutable binding in an
environment record. The String value <i>N</i>
is the text of the bound name. <i>V</i>
is the value for the binding and may be a value of any
ECMAScript <a href="x8.html#language-type">language type</a>. <i>S</i>
is a Boolean flag. If <i>S</i>
is <b>true</b> and
the binding cannot be set throw a <b><a href="x15.11.html#x15.11.6.5" class="term-ref">TypeError</a></b> exception. <i>S</i>
is used to identify strict mode references.</p>
</td>
</tr><tr valign="TOP"><td width="211">
<p>
GetBindingValue(N,S)</p>
</td>
<td width="445">
<p>
Returns
the value of an already existing binding from an environment
record. The String value <i>N</i>
is the text of the bound name. <i>S</i>
is used to identify strict mode references. If <i>S</i>
is <b>true</b> and
the binding does not exist or is uninitialized throw a
<b><a href="x15.11.html#x15.11.6.3" class="term-ref">ReferenceError</a></b> exception.
</p>
</td>
</tr><tr valign="TOP"><td width="211" height="58">
<p>
DeleteBinding(N)</p>
</td>
<td width="445">
<p>
Delete
a binding from an environment record. The String value <i>N</i>
is the text of the bound name If a binding for <i>N</i>
exists, remove the binding and return <b>true</b>. If the
binding exists but cannot be removed return <b>false</b>. If the
binding does not exist return <b>true</b>.</p>
</td>
</tr><tr valign="TOP"><td width="211">
<p>ImplicitThisValue()</p>
</td>
<td width="445">
<p>Returns
the value to use as the <b>this</b> value on calls to function
objects that are obtained as binding values from this
environment record.
</p>
</td>
</tr></tbody></table></center>
<h5 id="x10.2.1.1">10.2.1.1 Declarative Environment Records <a href="#x10.2.1.1">#</a> <a href="#x10.2.1.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h5>
<p>
Each
declarative environment record is associated with an ECMAScript
program scope containing variable and/or function declarations. A
declarative environment record binds the set of identifiers defined
by the declarations contained within its scope.</p>
<p class="sm-btm">
In
addition to the mutable bindings supported by all Environment
Records, declarative environment records also provide for immutable
bindings. An <dfn id="immutable-binding">immutable binding</dfn> is one where the association between
an identifier and a value may not be modified once it has been
established. Creation and initialization of immutable binding are
distinct steps so it is possible for such bindings to exist in
either an initialized or uninitialized state. Declarative
environment records support the methods listed in Table 18 in
addition to the Environment Record abstract specification methods:</p>
<center>
<table width="698" border="1" bordercolor="#000000" cellpadding="8" cellspacing="0" rules="ROWS"><caption>Table 18 — Additional Methods of Declarative Environment Records</caption>
<colgroup><col width="219"><col width="445"></colgroup><tbody><tr valign="TOP"><td width="219" height="8" bgcolor="#c0c0c0">
<p>
<i><b><span class="table-header">Method</span></b></i></p>
</td>
<td width="445" bgcolor="#c0c0c0">
<p>
<i><b><span class="table-header">Purpose</span></b></i></p>
</td>
</tr><tr valign="TOP"><td width="219">
<p>
<a href="#x10.2.1.1.7">CreateImmutableBinding</a>(N)</p>
</td>
<td width="445">
<p>
Create
a new but uninitialized <a href="#immutable-binding">immutable binding</a> in an environment
record. The String value <i>N</i>
is the text of the bound name.</p>
</td>
</tr><tr valign="TOP"><td width="219">
<p><a href="#x10.2.1.1.8">InitializeImmutableBinding</a>(N,V)</p>
</td>
<td width="445">
<p>Set
the value of an already existing but uninitialized <a href="#immutable-binding">immutable binding</a> in an environment record. The String value <i>N</i>
is the text of the bound name. <i>V</i>
is the value for the binding and is a value of any ECMAScript
<a href="x8.html#language-type">language type</a>.
</p>
</td>
</tr></tbody></table></center>
<p>
The
behaviour of the concrete specification methods for Declarative
Environment Records are defined by the following algorithms.</p>
<h6 id="x10.2.1.1.1">10.2.1.1.1 HasBinding(N) <a href="#x10.2.1.1.1">#</a> <a href="#x10.2.1.1.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete environment record method HasBinding for declarative
environment records simply determines if the argument identifier is
one of the identifiers bound by the record:</p>
<ol><li><p>
Let
<i>envRec </i>be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
If
<i>envRec</i> has a binding for the name that is the value of <i>N</i>,
return <b>true</b>.</p>
</li>
<li><p>
If
it does not have such a binding, return <b>false</b></p>
</li></ol><h6 id="x10.2.1.1.2">10.2.1.1.2 CreateMutableBinding (N, D) <a href="#x10.2.1.1.2">#</a> <a href="#x10.2.1.1.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method CreateMutableBinding for
declarative environment records creates a new mutable binding for
the name <i>N</i> that is
initialized to the value <b>undefined</b>. A binding must not
already exist in this Environment Record for <i>N</i>.
If Boolean argument <i>D</i>
is provided and has the value <b>true</b> the new binding is marked
as being subject to deletion.</p>
<ol><li><p>
Let
<i>envRec </i>be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
Assert:
<i>envRec</i> does not already have a binding for <i>N</i>.</p>
</li>
<li><p>
Create
a mutable binding in <i>envRec</i> for <i>N</i> and set its bound
value to <b>undefined</b>. If <i>D</i> is true record that the
newly created binding may be deleted by a subsequent DeleteBinding
call.</p>
</li></ol><h6 id="x10.2.1.1.3">10.2.1.1.3 SetMutableBinding (N,V,S) <a href="#x10.2.1.1.3">#</a> <a href="#x10.2.1.1.3-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method SetMutableBinding for declarative
environment records attempts to change the bound value of the
current binding of the identifier whose name is the value of the
argument <i>N</i> to the
value of argument <i>V</i>.
A binding for <i>N</i>
must already exist. If the binding is an <a href="#immutable-binding">immutable binding</a>, a
<b>TypeError</b> is
thrown
if <i>S</i> is <b>true</b>.
</p>
<ol><li><p>
Let
<i>envRec</i> be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
Assert:
<i>envRec</i> must have a binding for <i>N</i>.</p>
</li>
<li><p>
If
the binding for <i>N</i> in <i>envRec</i> is a mutable binding,
change its bound value to <i>V</i>.</p>
</li>
<li><p>
Else
this must be an attempt to change the value of an <a href="#immutable-binding">immutable binding</a>
so
if <i>S</i> is <b>true</b>
throw a
<b><a href="x15.11.html#x15.11.6.5" class="term-ref">TypeError</a></b>
exception.</p>
</li>
</ol><h6 id="x10.2.1.1.4">10.2.1.1.4 GetBindingValue(N,S) <a href="#x10.2.1.1.4">#</a> <a href="#x10.2.1.1.4-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method GetBindingValue for declarative
environment records simply returns the value of its bound identifier
whose name is the value of the argument <i>N</i>.
The binding must already exist. If <i>S</i>
is <b>true</b> and the binding is an uninitialized <a href="#immutable-binding">immutable binding</a>
throw a <b><a href="x15.11.html#x15.11.6.3" class="term-ref">ReferenceError</a></b> exception.</p>
<ol><li><p>
Let
<i>envRec</i> be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
Assert:
<i>envRec</i> has a binding for <i>N</i>.</p>
</li>
<li><p>
If
the binding for <i>N</i> in <i>envRec</i> is an uninitialized
<a href="#immutable-binding">immutable binding</a>, then</p>
<ol><li><p>
If
<i>S</i> is <b>false</b>, return the value <b>undefined</b>,
otherwise throw a <b><a href="x15.11.html#x15.11.6.3" class="term-ref">ReferenceError</a></b> exception.</p>
</li></ol></li>
<li><p>
Else,
return the value currently bound to <i>N</i> in <i>envRec</i>.</p>
</li></ol><h6 id="x10.2.1.1.5">10.2.1.1.5 DeleteBinding (N) <a href="#x10.2.1.1.5">#</a> <a href="#x10.2.1.1.5-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method DeleteBinding for declarative
environment records can only delete bindings that have been
explicitly designated as being subject to deletion.</p>
<ol><li><p>
Let
<i>envRec</i> be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
If
<i>envRec</i> does not have a binding for the name that is the
value of <i>N</i>, return <b>true</b>.</p>
</li>
<li><p>
If
the binding for <i>N</i> in <i>envRec</i> is cannot be deleted,
return <b>false</b>.</p>
</li>
<li><p>
Remove
the binding for <i>N</i> from <i>envRec</i>.</p>
</li>
<li><p>
Return
<b>true</b>.</p>
</li></ol><h6 id="x10.2.1.1.6">10.2.1.1.6 ImplicitThisValue() <a href="#x10.2.1.1.6">#</a> <a href="#x10.2.1.1.6-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
Declarative
Environment Records always return <b>undefined</b> as their
ImplicitThisValue.</p>
<ol><li><p>
Return
<b>undefined</b>.</p>
</li></ol><h6 id="x10.2.1.1.7">10.2.1.1.7 CreateImmutableBinding (N) <a href="#x10.2.1.1.7">#</a> <a href="#x10.2.1.1.7-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method CreateImmutableBinding for
declarative environment records creates a new <a href="#immutable-binding">immutable binding</a> for
the name <i>N</i> that is
initialized to the value <b>undefined</b>. A binding must not
already exist in this environment record for <i>N</i>.</p>
<ol><li><p>
Let
<i>envRec </i>be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
Assert:
<i>envRec </i>does not already have a binding for <i>N</i>.</p>
</li>
<li><p>
Create
an <a href="#immutable-binding">immutable binding</a> in <i>envRec</i> for <i>N</i> and record that
it is uninitialized.</p>
</li></ol><h6 id="x10.2.1.1.8">10.2.1.1.8 InitializeImmutableBinding (N,V) <a href="#x10.2.1.1.8">#</a> <a href="#x10.2.1.1.8-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method InitializeImmutableBinding for
declarative environment records is used to set the bound value of
the current binding of the identifier whose name is the value of the
argument <i>N</i> to the
value of argument <i>V</i>.
An uninitialized <a href="#immutable-binding">immutable binding</a> for <i>N</i>
must already exist.
</p>
<ol><li><p>
Let
<i>envRec </i>be the declarative environment record for which the
method was invoked.</p>
</li>
<li><p>
Assert:
<i>envRec</i> must have an uninitialized <a href="#immutable-binding">immutable binding</a> for N.</p>
</li>
<li><p>
Set
the bound value for <i>N</i> in <i>envRec</i> to <i>V</i>.</p>
</li>
<li><p>
Record
that the <a href="#immutable-binding">immutable binding</a> for <i>N</i> in <i>envRec</i> has been
initialized.</p>
</li></ol><h5 id="x10.2.1.2">10.2.1.2 Object Environment Records <a href="#x10.2.1.2">#</a> <a href="#x10.2.1.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h5>
<p>
Each
object environment record is associated with an object called its
<i>binding object</i>. An object environment record binds the set of
identifier names that directly correspond to the property names of
its binding object. Property names that are not an <i>IdentifierName </i>are not included in the set of bound identifiers. Both
own and inherited properties are included in the set regardless of
the setting of their [[Enumerable]] attribute. Because properties
can be dynamically added and deleted from objects, the set of
identifiers bound by an object environment record may potentially
change as a side-effect of any operation that adds or deletes
properties. Any bindings that are created as a result of such a
side-effect are considered to be a mutable binding even if the
Writable attribute of the corresponding property has the value
<b>false</b>. Immutable bindings do not exist for object environment
records.</p>
<p>
Object
environment records can be configured to provide their binding
object as an implicit this value for use in function calls. This
capability is used to specify the behaviour of With Statement
(<a href="x12.html#x12.10">12.10</a>) induced bindings. The capability is controlled by a
<i>provideThis</i>
Boolean value that is associated with each object environment
record. By default, the value of <i>provideThis</i>
is <b>false</b> for any object environment record.</p>
<p>
The
behaviour of the concrete specification methods for Object
Environment Records is defined by the following algorithms.</p>
<h6 id="x10.2.1.2.1">10.2.1.2.1 HasBinding(N) <a href="#x10.2.1.2.1">#</a> <a href="#x10.2.1.2.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method HasBinding for object environment
records determines if its associated <a href="#x10.2.1.2">binding object</a> has a property
whose name is the value of the argument <i>N</i>:</p>
<ol><li><p>
Let
<i>envRec </i>be the object environment record for which the method
was invoked.</p>
</li>
<li><p>
Let
<i>bindings </i>be the <a href="#x10.2.1.2">binding object</a> for <i>envRec</i>.</p>
</li>
<li><p>
Return
the result of calling the [[HasProperty]] internal method of
<i>bindings</i>, passing <i>N</i> as the property name.</p>
</li></ol><h6 id="x10.2.1.2.2">10.2.1.2.2 CreateMutableBinding (N, D) <a href="#x10.2.1.2.2">#</a> <a href="#x10.2.1.2.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method CreateMutableBinding for object
environment records creates in an environment record’s associated
<a href="#x10.2.1.2">binding object</a> a property whose name is the String value and
initializes it to the value <b>undefined</b>. A property named <i>N</i>
must not already exist in the <a href="#x10.2.1.2">binding object</a>. If Boolean argument <i>D</i>
is provided and has the value <b>true</b> the new property’s
[[Configurable]] attribute is set to <b>true</b>, otherwise it is
set to <b>false</b>.</p>
<ol><li><p>
Let
<i>envRec</i> be the object environment record for which the method
was invoked.</p>
</li>
<li><p>
Let
<i>bindings</i> be the <a href="#x10.2.1.2">binding object</a> for <i>envRec</i>.</p>
</li>
<li><p>
Assert:
The result of calling the [[HasProperty]] internal method of
<i>bindings</i>, passing <i>N</i> as the property name, is <b>false</b>.</p>
</li>
<li><p>
If
D is <b>true</b> then let <i>configValue</i> be <b>true</b>
otherwise let <i>configValue</i> be <b>false</b>.</p>
</li>
<li><p>
Call
the [[DefineOwnProperty]] internal method of <i>bindings</i>,
passing <i>N</i>, <a href="x8.html#x8.10">Property Descriptor</a> {[[Value]]:<b>undefined</b>,
[[Writable]]: <b>true</b>, [[Enumerable]]: <b>true</b> ,
[[Configurable]]: <i>configValue</i>}, and
<b>true</b>
as
arguments.</p>
</li>
</ol><h6 id="x10.2.1.2.3">10.2.1.2.3 SetMutableBinding (N,V,S) <a href="#x10.2.1.2.3">#</a> <a href="#x10.2.1.2.3-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method SetMutableBinding for object
environment records attempts to set the value of the environment
record’s associated <a href="#x10.2.1.2">binding object</a>’s property whose name is the
value of the argument <i>N</i>
to the value of argument <i>V</i>.
A property named <i>N</i>
should already exist but if it does not or is not currently
writable, error handling is determined by the value of the Boolean
argument <i>S</i>.</p>
<ol><li><p>
Let
<i>envRec</i> be the object environment record for which the method
was invoked.</p>
</li>
<li><p>
Let
<i>bindings</i> be the <a href="#x10.2.1.2">binding object</a> for <i>envRec</i>.</p>
</li>
<li><p>
Call
the [[Put]] internal method of <i>bindings</i> with arguments <i>N</i>,
<i>V</i>, and <i>S</i>.</p>
</li></ol><h6 id="x10.2.1.2.4">10.2.1.2.4 GetBindingValue(N,S) <a href="#x10.2.1.2.4">#</a> <a href="#x10.2.1.2.4-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method GetBindingValue for object
environment records returns the value of its associated <a href="#x10.2.1.2">binding object</a>’s property whose name is the String value of the argument
identifier <i>N</i>. The
property should already exist but if it does not the result depends
upon the value of the <i>S</i>
argument:</p>
<ol><li><p>
Let
<i>envRec</i> be the object environment record for which the method
was invoked.</p>
</li>
<li><p>
Let
<i>bindings</i> be the <a href="#x10.2.1.2">binding object</a> for <i>envRec</i>.</p>
</li>
<li><p>
Let
<i>value</i> be the result of calling the [[HasProperty]] internal
method of <i>bindings</i>, passing <i>N</i> as the property name.</p>
</li>
<li><p>
If
<i>value</i> is <b>false</b>, then</p>
<ol><li><p>
If
<i>S</i> is <b>false</b>, return the value <b>undefined</b>,
otherwise throw a <b>ReferenceError </b>exception.</p>
</li></ol></li>
<li><p>
Return
the result of calling the [[Get]] internal method of <i>bindings</i>,
passing <i>N</i> for the argument.</p>
</li></ol><h6 id="x10.2.1.2.5">10.2.1.2.5 DeleteBinding (N) <a href="#x10.2.1.2.5">#</a> <a href="#x10.2.1.2.5-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
The
concrete Environment Record method DeleteBinding for object
environment records can only delete bindings that correspond to
properties of the environment object whose [[Configurable]]
attribute have the value <b>true</b>.</p>
<ol><li><p>
Let
<i>envRec</i> be the object environment record for which the method
was invoked.</p>
</li>
<li><p>
Let
<i>bindings </i>be the <a href="#x10.2.1.2">binding object</a> for <i>envRec</i>.</p>
</li>
<li><p>
Return
the result of calling the [[Delete]] internal method of <i>bindings</i>,
passing <i>N</i> and <b>false</b> as arguments.</p>
</li></ol><h6 id="x10.2.1.2.6">10.2.1.2.6 ImplicitThisValue() <a href="#x10.2.1.2.6">#</a> <a href="#x10.2.1.2.6-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h6>
<p>
Object
Environment Records return <b>undefined</b> as their
ImplicitThisValue unless their <i>provideThis</i>
flag is <b>true</b>.</p>
<ol><li><p>
Let
<i>envRec</i> be the object environment record for which the method
was invoked.</p>
</li>
<li><p>
If
the <i>provideThis</i> flag of <i>envRec</i> is <b>true</b>, return
the <a href="#x10.2.1.2">binding object</a> for <i>envRec</i>.</p>
</li>
<li><p>
Otherwise,
return <b>undefined</b>.</p>
</li></ol><h4 id="x10.2.2">10.2.2 Lexical Environment Operations <a href="#x10.2.2">#</a> <a href="#x10.2.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
The
following abstract operations are used in this specification to
operate upon lexical environments:</p>
<h5 id="x10.2.2.1">10.2.2.1 GetIdentifierReference (lex, name, strict) <a href="#x10.2.2.1">#</a> <a href="#x10.2.2.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h5>
<p>
The
abstract operation GetIdentifierReference is called with a <a href="#x10.2">Lexical Environment</a> <i>lex</i>,
an identifier String <i>name</i>,
and a Boolean flag <i>strict. </i>The value of <i>lex </i>may be <b>null</b>. When called, the following steps are
performed:</p>
<ol><li><p>
If
<i>lex</i> is the value <b>null</b>, then</p>
<ol><li><p>
Return
a value of type <a href="x8.html#x8.7">Reference</a> whose base value is <b>undefined</b>,
whose referenced name is <i>name</i>, and whose strict mode flag
is <i>strict</i>.</p>
</li></ol></li>
<li><p>
Let
<i>envRec</i> be <i>lex</i>’s environment record.</p>
</li>
<li><p>
Let
<i>exists </i>be the result of calling the HasBinding(<i>N</i>)
concrete method of <i>envRec</i> passing <i>name</i> as the
argument <i>N</i>.</p>
</li>
<li><p>
If
<i>exists </i>is <code><b>true</b></code>,
then</p>
<ol><li><p>
Return
a value of type <a href="x8.html#x8.7">Reference</a> whose base value is <i>envRec</i>, whose
referenced name is <i>name</i>, and whose strict mode flag is
<i>strict.</i></p>
</li></ol></li>
<li><p>
Else</p>
<ol><li><p>
Let
<i>outer </i>be the value of <i>lex’s</i> <a href="#outer-environment-reference">outer environment reference</a>.</p>
</li>
<li><p>
Return
the result of calling GetIdentifierReference passing <i>outer</i>,
<i>name</i>, and <i>strict</i> as arguments.</p>
</li></ol></li></ol><h5 id="x10.2.2.2">10.2.2.2 NewDeclarativeEnvironment (E) <a href="#x10.2.2.2">#</a> <a href="#x10.2.2.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h5>
<p>
When
the abstract operation NewDeclarativeEnvironment is called with
either a <a href="#x10.2">Lexical Environment</a> or <b>null</b> as argument <i>E </i>the following steps are performed:</p>
<ol><li><p>
Let
<i>env</i> be a new <a href="#x10.2">Lexical Environment</a>.</p>
</li>
<li><p>
Let
<i>envRec</i> be a new <a href="#declarative-environment-record">declarative environment record</a> containing no
bindings.</p>
</li>
<li><p>
Set
<i>env’s</i> environment record to be <i>envRec</i>.</p>
</li>
<li><p>
Set
the outer lexical environment reference of <i>env</i> to <i>E</i>.</p>
</li>
<li><p>
Return
<i>env</i>.</p>
</li></ol><h5 id="x10.2.2.3">10.2.2.3 NewObjectEnvironment (O, E) <a href="#x10.2.2.3">#</a> <a href="#x10.2.2.3-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h5>
<p>
When
the abstract operation NewObjectEnvironmentis called with an Object
<i>O</i> and a <a href="#x10.2">Lexical Environment</a> <i>E </i>(or
<b>null)</b> as arguments, the following steps are performed:</p>
<ol><li><p>
Let
<i>env</i> be a new <a href="#x10.2">Lexical Environment</a>.</p>
</li>
<li><p>
Let
<i>envRec</i> be a new <a href="#object-environment-record">object environment record</a> containing <i>O</i>
as the <a href="#x10.2.1.2">binding object</a>.</p>
</li>
<li><p>
Set
<i>env’s</i> environment record to be <i>envRec</i>.</p>
</li>
<li><p>
Set
the outer lexical environment reference of <i>env</i> to <i>E</i>.</p>
</li>
<li><p>
Return
<i>env</i>.</p>
</li></ol><h4 id="x10.2.3">10.2.3 The Global Environment <a href="#x10.2.3">#</a> <a href="#x10.2.3-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
The
<i>global environment</i> is a unique <a href="#x10.2">Lexical Environment</a> which is
created before any ECMAScript code is executed. The global
environment’s <a href="#x10.2.1">Environment Record</a> is an <a href="#object-environment-record">object environment record</a>
whose <a href="#x10.2.1.2">binding object</a> is the <a href="x15.1.html#x15.1" class="term-ref">global object</a> (<a href="x15.1.html#x15.1">15.1</a>). The global
environment’s <a href="#outer-environment-reference">outer environment reference</a> is <b>null</b>.</p>
<p>
As
ECMAScript code is executed, additional properties may be added to
the <a href="x15.1.html#x15.1" class="term-ref">global object</a> and the initial properties may be modified.
</p>
<h3 id="x10.3">10.3 Execution Contexts <a href="#x10.3">#</a> <a href="#x10.3-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h3>
<p>
When
control is transferred to ECMAScript executable code, control is
entering an <i>execution context</i>. Active execution contexts
logically form a stack. The top execution context on this logical
stack is the running execution context. A new execution context is
created whenever control is transferred from the executable code
associated with the currently running execution context to
executable code that is not associated with that execution context.
The newly created execution context is pushed onto the stack and
becomes the running execution context.</p>
<p>
An
execution context contains whatever state is necessary to track the
execution progress of its associated code. In addition, each
execution context has the state components listed in Table 19.</p>
<center>
<table width="690" border="1" bordercolor="#000000" cellpadding="8" cellspacing="0" rules="ROWS"><caption>Table 19 —Execution Context State Components</caption>
<colgroup><col width="161"><col width="495"></colgroup><tbody><tr valign="TOP"><td width="161" height="11" bgcolor="#c0c0c0">
<p>
<i><b><span class="table-header">Component</span></b></i></p>
</td>
<td width="495" bgcolor="#c0c0c0">
<p>
<i><b><span class="table-header">Purpose</span></b></i></p>
</td>
</tr><tr valign="TOP"><td width="161">
<p>
LexicalEnvironment</p>
</td>
<td width="495">
<p>
Identifies
the <a href="#x10.2">Lexical Environment</a> used to resolve identifier references
made by code within this execution context.</p>
</td>
</tr><tr valign="TOP"><td width="161">
<p>
VariableEnvironment</p>
</td>
<td width="495">
<p>
Identifies
the <a href="#x10.2">Lexical Environment</a> whose environment record holds bindings
created by <i>VariableStatements</i>
and <i>FunctionDeclarations</i>
within this execution context.</p>
</td>
</tr><tr valign="TOP"><td width="161">
<p>ThisBinding</p>
</td>
<td width="495">
<p>The
value associated with the <code><b>this</b></code>
keyword within ECMAScript code associated with this execution
context.</p>
</td>
</tr></tbody></table></center>
<p>
The
LexicalEnvironment and VariableEnvironment components of an
execution context are always <a href="#x10.2">Lexical Environment</a>s. When an execution
context is created its LexicalEnvironment and VariableEnvironment
components initially have the same value. The value of the
VariableEnvironment component never changes while the value of the
LexicalEnvironment component may change during execution of code
within an execution context.</p>
<p>
In
most situations only the running execution context (the top of the
execution context stack) is directly manipulated by algorithms
within this specification. Hence when the terms
“LexicalEnvironment”, “VariableEnvironment” and
“ThisBinding” are used without qualification they are in
reference to those components of the running execution context.</p>
<p>
An
execution context is purely a specification mechanism and need not
correspond to any particular artefact of an ECMAScript
implementation. It is impossible for an ECMAScript program to
access an execution context.
</p>
<h4 id="x10.3.1">10.3.1 Identifier Resolution <a href="#x10.3.1">#</a> <a href="#x10.3.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
Identifier
resolution is the process of determining the binding of an
<i>Identifier</i> using
the <a href="#x10.2">LexicalEnvironment</a> of the running execution context. During
execution of ECMAScript code, the syntactic production
<i>PrimaryExpression</i>
<b>:</b>
<i>Identifier</i> is
evaluated using the following algorithm:</p>
<ol><li><p>
Let
<i>env</i> be the running execution context’s <a href="#x10.2">LexicalEnvironment</a>.</p>
</li>
<li><p>
If
the syntactic production that is being evaluated is contained in a
<a href="#x10.1.1" class="term-ref">strict mode code</a>, then let <i>strict</i> be <b>true</b>, else let
<i>strict</i> be <b>false</b>.</p>
</li>
<li><p>
Return
the result of calling <a href="#x10.2.2.1">GetIdentifierReference</a> function passing <i>env</i>,
<i>Identifier</i>, and <i>strict</i> as arguments.</p>
</li></ol><p>
The
result of evaluating an identifier is always a value of type
<a href="x8.html#x8.7">Reference</a> with its referenced name component equal to the <i>Identifier</i>
String.</p>
<h3 id="x10.4">10.4 Establishing an Execution Context <a href="#x10.4">#</a> <a href="#x10.4-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h3>
<p>
Evaluation
of <a href="#global-code">global code</a> or code using the eval function (<a href="x15.1.html#x15.1.2.1">15.1.2.1</a>)
establishes and enters a new execution context. Every invocation of
an ECMAScript code function (<a href="x13.html#x13.2.1">13.2.1</a>) also establishes and enters a
new execution context, even if a function is calling itself
recursively. Every return exits an execution context. A thrown
exception may also exit one or more execution contexts.</p>
<p>
When
control enters an execution context, the execution context’s
ThisBinding is set, its VariableEnvironment and initial
LexicalEnvironment are defined, and declaration binding
instantiation (<a href="#x10.5">10.5</a>) is performed. The exact manner in which these
actions occur depend on the type of code being entered.</p>
<h4 id="x10.4.1">10.4.1 Entering Global Code <a href="#x10.4.1">#</a> <a href="#x10.4.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
The
following steps are performed when control enters the execution
context for <a href="#global-code">global code</a>:</p>
<ol><li><p>
Initialize
the execution context using the <a href="#global-code">global code</a> as described in
<a href="#x10.4.1.1">10.4.1.1</a>.</p>
</li>
<li><p>
Perform
Declaration Binding Instantiation as described in <a href="#x10.5">10.5</a> using the
<a href="#global-code">global code</a>.</p>
</li></ol><h5 id="x10.4.1.1">10.4.1.1 Initial Global Execution Context <a href="#x10.4.1.1">#</a> <a href="#x10.4.1.1-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h5>
<p>
The
following steps are performed to initialize a global execution
context for ECMAScript code <i>C</i>:</p>
<ol><li><p>
Set
the VariableEnvironment to the <a href="#x10.2.3">Global Environment</a>.</p>
</li>
<li><p>
Set
the LexicalEnvironment to the <a href="#x10.2.3">Global Environment</a>.</p>
</li>
<li><p>
Set
the ThisBinding to the <a href="x15.1.html#x15.1" class="term-ref">global object</a>.</p>
</li></ol><h4 id="x10.4.2">10.4.2 Entering Eval Code <a href="#x10.4.2">#</a> <a href="#x10.4.2-toc" class="bak">Ⓣ</a> <b class="erra">Ⓔ</b> <b class="rev1">①</b> <b class="anno">Ⓐ</b></h4>
<p>
The
following steps are performed when control enters the execution
context for <a href="#eval-code">eval code</a>:</p>
<ol><li><p>
If
there is no calling context or if the <a href="#eval-code">eval code</a> is not being
evaluated by a direct call (<a href="x15.1.html#x15.1.2.1.1">15.1.2.1.1</a>) to the eval function then,</p>
<ol><li><p>
Initialize
the execution context as if it was a global execution context
using the <a href="#eval-code">eval code</a> as <i>C</i> as described in <a href="#x10.4.1.1">10.4.1.1</a>.</p>
</li></ol></li>
<li><p>
Else,</p>
<ol><li><p>
Set