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<pre class="metadata">
title: ECMAScript Try Operator
stage: -1
contributors: Arthur Fiorette, Arlen Beiler
</pre>

<emu-biblio href="node_modules/@tc39/ecma262-biblio/biblio.json"></emu-biblio>

<emu-clause id="sec-assignment-operators">
  <h1>Assignment Operators</h1>
  <h2>Syntax</h2>
  <emu-grammar type="definition">
    AssignmentExpression[In, Yield, Await] :
      TryExpression[?In, ?Yield, ?Await]
    TryExpression[In, Yield, Await] :
      `try` [no LineTerminator here] [lookahead != `{`] AssignmentExpression[?In, ?Yield, ?Await]
  </emu-grammar>

  <emu-clause id="sec-comma-operator-runtime-semantics-evaluation" type="sdo">
    <h1>Runtime Semantics: Evaluation</h1>
    <emu-grammar>TryExpression : `try` AssignmentExpression</emu-grammar>
    <emu-alg>
      1. Let _A_ be Completion(Evaluation of |Expression|).
      1. If _A_ is an abrupt completion, return ? TryExpressionResult(_A_).
      1. Let _B_ be Completion(GetValue(_A_)).
      1. Return ? TryExpressionResult(_B_).
    </emu-alg>
    <emu-note>
      <p>GetValue must be called even though its value is not used because it may have observable side-effects.</p>
    </emu-note>
  </emu-clause>

  <emu-clause id="sec-try-expression-result" type="abstract operation">
    <h1>
      TryExpressionResult (
        _result_: a Completion Record,
      ): either a normal completion containing a Result or an abrupt completion
    </h1>
    <dl class="header">
    </dl>
    <emu-alg>
      1. If _result_ is a normal completion, return Result.ok(_result_.[[VALUE]]).
      1. If _result_ is a throw completion, return Result.error(_result_.[[VALUE]]).
      1. Return ? _result_.
    </emu-alg>
  </emu-clause>
  <emu-clause id="sec-try-expression-result-ok" type="abstract operation">
    <h1>
      Result.ok (
        _value_: an ECMAScript language value,
      ): a Result
    </h1>
    <dl class="header">
      <dt>description</dt>
      <dd>It is the abstract equivelant of calling `Result.ok(value)`</dd>
    </dl>
  </emu-clause>
  <emu-clause id="sec-try-expression-result-error" type="abstract operation">
    <h1>
      Result.error (
        _value_: an ECMAScript language value,
      ): a Result
    </h1>
    <dl class="header">
      <dt>description</dt>
      <dd>It is the abstract equivelant of calling `Result.error(value)`</dd>
    </dl>
  </emu-clause>
</emu-clause>

<emu-clause id="sec-well-known-intrinsic-objects">
  <h1>Well-Known Intrinsic Objects</h1>
  <emu-table id="table-well-known-intrinsic-objects" caption="Well-Known Intrinsic Objects" oldids="table-7">
    <table>
      <thead>
        <tr>
          <th>
            Intrinsic Name
          </th>
          <th>
            Global Name
          </th>
          <th>
            ECMAScript Language Association
          </th>
        </tr>
      </thead>
      <tr>
        <td>
          %Result%
        </td>
        <td>
          `Result`
        </td>
        <td>
          The `Result` constructor (<emu-xref href="#sec-result-constructor"></emu-xref>)
        </td>
      </tr>
    </table>
  </emu-table>
</emu-clause>

<emu-clause id="sec-result-constructor">
  <h1>The Result Constructor</h1>
  <p>The Result constructor:</p>
  <ul>
    <li>is <dfn variants="Result">%Result%</dfn>.</li>
    <li>is the initial value of the *"Result"* property of the global object.</li>
    <li>is the functional equivelant of the following code:
      <pre><code class="javascript">
        class Result {
          constructor(ok, error, value) {
            this.ok = ok
            this.error = error
            this.value = value
          }
          *[Symbol.iterator]() {
            yield this.ok
            yield this.error
            yield this.value
          }
          static ok(value) {
            return new Result(true, undefined, value)
          }
          static error(error) {
            return new Result(false, error, undefined)
          }
        }
      </code></pre>
    </li>
  </ul>
</emu-clause>