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regExp.sticky

The sticky property reflects whether or not the search is sticky (searches in strings only from the index indicated by the lastIndex property of this regular expression). sticky is a read-only property of an individual regular expression object.

Property attributes of RegExp.prototype.sticky
Writable no
Enumerable no
Configurable yes

Description

The value of sticky is a Boolean and true if the "y" flag was used; otherwise, false. The "y" flag indicates that it matches only from the index indicated by the lastIndex property of this regular expression in the target string (and does not attempt to match from any later indexes). A regular expression defined as both sticky and global ignores the global flag.

You cannot change this property directly. It is read-only.

Examples

Using a regular expression with the sticky flag

var str = '#foo#';
var regex = /foo/y;

regex.lastIndex = 1;
regex.test(str); // true
regex.lastIndex = 5;
regex.test(str); // false (lastIndex is taken into account with sticky flag)
regex.lastIndex; // 0 (reset after match failure)

Anchored sticky flag

For several versions, Firefox's SpiderMonkey engine had a bug with regard to the ^ assertion and the sticky flag which allowed expressions starting with the ^ assertion and using the sticky flag to match when they shouldn't. The bug was introduced some time after Firefox 3.6 (which had the sticky flag but not the bug) and fixed in 2015. Perhaps because of the bug, the ES2015 specification specifically calls out the fact that:

When the y flag is used with a pattern, ^ always matches only at the beginning of the input, or (if multiline is true) at the beginning of a line.

Examples of correct behavior:

var regex = /^foo/y;
regex.lastIndex = 2;
regex.test('..foo');   // false - index 2 is not the beginning of the string

var regex2 = /^foo/my;
regex2.lastIndex = 2;
regex2.test('..foo');  // false - index 2 is not the beginning of the string or line
regex2.lastIndex = 2;
regex2.test('.\nfoo'); // true - index 2 is the beginning of a line

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 49 13 3 No 36 10
Prototype accessor property (ES2015) Yes ? 38 ? Yes Yes
Anchored sticky flag behavior per ES2015 Yes Yes 44 No Yes Yes
Mobile
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support 49 49 Yes 4 36 10 5.0
Prototype accessor property (ES2015) Yes Yes ? 38 Yes Yes Yes
Anchored sticky flag behavior per ES2015 ? Yes Yes 44 ? ? Yes
Server
Node.js
Basic support Yes
Prototype accessor property (ES2015) Yes
Anchored sticky flag behavior per ES2015 ?

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/sticky