Esvisit

Esvisit is a simple npm module for visiting JavaScript abstract syntax trees that are compatible with Mozilla parser API as described in https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Parser_API#Programs. This module supports exclusvely ECMAScript5 as described in http://www.ecma-international.org/ecma-262/5.1/. Benefits of using Esvisit includes:

• Process iteratively and avoid recursion.
• Get an alternative type that better reflects JavaScript semantic.
• Visit only actual statements and expressions.

Demonstration

var Esvisit = require('esvisit');
var Esprima = require('esprima');

function indent () { return (new Array(depth+1)).join("  ") }
function visitStatement (type, stmt) { visit('Statement', type, stmt) }
function visitExpression (type, expr) { visit('Expression', type, expr) }
function visit (kind, type, node) {
  var id = ++counter;
  console.log(indent()+'Begin'+kind+id+': '+type+'('+Esvisit.ExtractInformation(type, node).join(", ")+')')
  depth++
  push(function () {
    depth--
    console.log(indent()+'End'+id)
  })
}

var code = 'o.a = eval("2*"+x);' // Your JS code here...
var ast = Esprima.parse(code)
var counter = 0;
var depth = 0;
var push = Esvisit.Prepare(visitStatement, visitExpression)

push(ast)

Output:

BeginStatement1: Expression()
  BeginExpression2: MemberAssignment(a, =)
    BeginExpression3: EvalCall(1)
      BeginExpression4: Binary(+)
        BeginExpression5: Literal(2*)
        End5
        BeginExpression6: Identifier(x)
        End6
      End4
    End3
    BeginExpression7: Identifier(o)
    End7
  End2
End1

API

This module exposes four functions:

• Prepare(StatementCallback, ExpressionCallBack): prepare upcoming visits ; returns a function to push something on the worker list. Callbacks are called with: the Esvisit type of the current node and the current node itself. Esvisit types are described in the sections 'Statement Types' and 'Expression Types'
• ExtractInformation(EsvisitType, Node)
• ExtractStatementInformation(EsvisitType, Statement)
• ExtractExpressionInformation(EsvisitType, Expression)

Statement Types

Type	Interpretation	Information
Empty	alias for EmptyStatement	[]
Strict	'use strict';	[]
Block	*	[Length]
Expression	*	[]
If	*	[HasAlternate]
Label	*	[Label]
Break	*	[MaybeLabel]
Continue	*	[MaybeLabel]
With	*	[]
Switch	*	[Cases::[IsDefault, Length]]
Return	*	[HasValue]
Throw	*	[]
Try	*	[BodyLength, MaybeCatchParameter, MaybeCatchLength, MaybeFinalizerLength]
While	*	[]
DoWhile	*	[]
DeclarationFor	for (VAR_DECL; EXPR; EXPR) STMT	[Declarators::[Name, HasInit], HasTest, HasUpdate]
For	for (EXPR; EXPR; EXPR) STMT	[HasInit, HasTest, HasUpdate]
IdentifierForIn	for (ID in EXPR) STMT	[Name]
MemberForIn	for (MEMBER in EXPR) STMT	[MaybeProperty]
DeclarationForIn	for (var ID [=EXPR] in EXPR) STMT	[Name, HasInit]
Definition	alias for FunctionDeclaration	[Name, Parameters::[Name], BodyLength]
Declaration	alias for VariableDeclaration	[Declarators::[Name, HasInit]]

(*): Add Statement to the type to obtain the Mozilla alias.

Expression Types

Type	Interpretation	Information
This	alias for ThisExpression	[]
Array	**	[Elements::[IsInitialized]]
Object	**	[Properties::[KeyValue, Kind, MaybeParameter, MaybeBodyLength]]
Function	**	[MaybeName, Parameters::[Name], BodyLength]
Sequence	**	[Length]
IdentifierTypeof	typeof ID	[Name]
IdentifierDelete	delete ID	[Name]
MemberDelete	delete MEMBER	[MaybeProperty]
Unary	**	[Operator]
Binary	**	[Operator]
IdentifierAssignment	ID ASS_OP EXPR	[Name, Operator]
MemberAssignment	MEMBER ASS_OP EXPR	[MaybeProperty, Operator]
IdentifierUpdate	++ID, --ID, ID++, ID--	[IsPrefix, Operator, Name]
MemberUpdate	++MEMBER, --MEMBER, MEMBER++, MEMBER--	[IsPrefix, Operator, MaybeProperty]
Logical	**	[Operator]
Conditional	**	[]
New	**	[ArgumentsLength]
MemberCall	MEMBER(EXPRS)	[MaybeProperty, ArgumentsLength]
EvalCall	eval(EXPRS)	[ArgumentsLength]
Call	EXPR(EXPRS)	[ArgumentsLength]
Member	**	[MaybeProperty]
Identifier	alias for Identifier	[Name]
Literal	alias for Literal	[Value]

(**): Add Expression to the type to obtain the Mozilla alias.