The source property returns a String containing the source text of the regexp object, and it doesn't contain the two forward slashes on both sides and any flags.

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


Using source

var regex = /fooBar/ig;

console.log(regex.source); // "fooBar", doesn't contain /.../ and "ig".

Empty regular expressions and escaping

Starting with ECMAScript 5, the source property no longer returns an empty string for empty regular expressions. Instead, the string "(?:)" is returned. In addition, line terminators (such as "\n") are escaped now.

new RegExp().source; // "(?:)"

new RegExp('\n').source === "\n";  // true, prior to ES5
new RegExp('\n').source === "\\n"; // true, starting with ES5


Specification Status Comment
ECMAScript 3rd Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.2. JavaScript 1.5: source is a property of a RegExp instance, not the RegExp object.
ECMAScript 5.1 (ECMA-262)
The definition of 'RegExp.prototype.source' in that specification.
Standard The source property for empty regular expressions now returns "(?:)" instead of an empty string. A definition for the escaping behavior has been added.
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'RegExp.prototype.source' in that specification.
Standard source is now a prototype accessor property rather than an instance's own data property.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'RegExp.prototype.source' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
"(?:)" for empty regexps ? 38 (38) ? ? (Yes)
Escaping ? 38 (38) ? ? ?
Prototype accessor property ? 41 (41) ? ? ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)
"(?:)" for empty regexps ? ? 38.0 (38) ? ? ?
Escaping ? ? 38.0 (38) ? ? ?
Prototype accessor property ? ? 41.0 (41) ? ? ?

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

JavaScript Property Prototype Reference RegExp Regular Expressions