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optional-catch

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Stage 4
Classification: Syntactic Change Semantic Change
Human Validated: KW
Title: Optional catch binding
Authors: Michael Ficarra
Champions: Michael Ficarra
Last Presented: May 2018
Stage Upgrades:
Stage 1: NA
Stage 2: NA
Stage 2.7: NA
Stage 3: 2017-07-28
Stage 4: 2018-05-22
Last Commit: 2018-05-22
Topics: others
Keywords: grammar error_handling error
GitHub Link: https://github.com/tc39/proposal-optional-catch-binding
GitHub Note Link: https://github.com/tc39/notes/blob/HEAD/meetings/2018-05/may-22.md#conclusionresolution-7

Proposal Description:

This proposal makes a grammatical change to ECMAScript, allowing the omission of a catch binding in cases where the binding would not be used. This occurs frequently with patterns such as

try {
  // try to use a web feature which may not be implemented
} catch (unused) {
  // fall back to a less desirable web feature with broader support
}

or

let isTheFeatureImplemented = false;
try {
  // stress the required bits of the web API
  isTheFeatureImplemented = true;
} catch (unused) {}

or

let parseResult = someFallbackValue;
try {
  parseResult = JSON.parse(potentiallyMalformedJSON);
} catch (unused) {}

and it is a common opinion that variables which are declared or written to but never read signify a programming error.

The grammar change introduced by this proposal allows for the catch binding and its surrounding parentheses to be omitted, as in

try {
  // ...
} catch {
  // ...
}

See the the full text of the proposal for more info.

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