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Asked: 2026-06-06T14:38:09+00:00

I read in Javascript: The Good Parts by Douglas Crockford that javascript regular expression

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I read in Javascript: The Good Parts by Douglas Crockford that javascript regular expression literals share the same object. If so, then how come these two regex literals vary in the lastIndex property?

var a = /a/g;
var b = /a/g;

a.lastIndex = 3;
document.write(b.lastIndex);​

JS Fiddle

0 is outputted as opposed to 3.

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1 Answer

  1. Editorial Team

    Section 7.8.5 of the ECMAScript Documentation makes it quite clear they are two different objects:

    7.8.5 Regular Expression Literals
    A regular expression literal is an input element that is converted to a RegExp object (see 15.10) each time the literal is evaluated. Two regular expression literals in a program evaluate to regular expression objects that never compare as === to each other even if the two literals’ contents are identical. A RegExp object may also be created at runtime by new RegExp (see 15.10.4) or calling the RegExp constructor as a function (15.10.3).

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