RegExp.prototype.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.

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).

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

This behavior was specified in ES2015 and differs from a previous Firefox implementation: "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".

var regex = /^foo/y;
regex.lastIndex = 2; // disallows to match at the beginning of the string
regex.test("..foo"); // false

var regex2 = /^foo/my;
regex2.lastIndex = 2;
regex2.test("..foo"); // false
regex2.lastIndex = 2;
regex2.test(".\nfoo"); // true

Specifications

Browser compatibility

See also

• RegExp.lastIndex
• RegExp.prototype.global
• RegExp.prototype.ignoreCase
• RegExp.prototype.multiline
• RegExp.prototype.source