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Editorial Team
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Asked: 2026-05-23T22:11:06+00:00

Is the following code valid? function test() { return /\//.exec(\/); } alert(test()); It seems

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Is the following code valid?

function test() {
  return /\//.exec("\/");
}
alert(test());

It seems that many javascript minifiers (including jsmin at http://jscompress.com/) consider the “//” on the second line to be the start of a comment. I assume it’s a bug in the “trivially” implemented minifiers, since all the browser implementations I tried run it without a problem. Try it on jsfiddle.

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1 Answer

  1. Editorial Team

    I was interested in looking it up in the specs, and according to it it is valid:

    RegularExpressionLiteral ::
    / RegularExpressionBody / RegularExpressionFlags
RegularExpressionBody ::
    RegularExpressionFirstChar RegularExpressionChars
RegularExpressionChars ::
    [empty]
    RegularExpressionChars RegularExpressionChar
RegularExpressionFirstChar ::
    RegularExpressionNonTerminator but not * or \ or / or [
    RegularExpressionBackslashSequence
    RegularExpressionClass
RegularExpressionChar ::
    RegularExpressionNonTerminator but not \ or / or [
    RegularExpressionBackslashSequence
    RegularExpressionClass
RegularExpressionBackslashSequence ::
    \ RegularExpressionNonTerminator
RegularExpressionNonTerminator ::
    SourceCharacter but not LineTerminator

    The \/ is considered a RegularExpressionBackslashSequence, and hence is part of RegularExpressionBody, and as a result cannot be part of the // comment marker.

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