RegExp.prototype.toString()
 The toString() method returns a string representing the regular expression. 
Syntax
toString()
Return value
A string representing the given object.
Description
 The RegExp object overrides the toString() method of the Object object; it does not inherit Object.prototype.toString(). For RegExp objects, the toString() method returns a string representation of the regular expression. 
Examples
Using toString()
The following example displays the string value of a RegExp object:
var myExp = new RegExp('a+b+c'); console.log(myExp.toString()); // logs '/a+b+c/' var foo = new RegExp('bar', 'g'); console.log(foo.toString()); // logs '/bar/g'
Empty regular expressions and escaping
Starting with ECMAScript 5, an empty regular expression returns the string "/(?:)/" and line terminators such as "\n" are escaped:
new RegExp().toString(); // "/(?:)/" new RegExp('\n').toString() === '/\n/'; // true, prior to ES5 new RegExp('\n').toString() === '/\\n/'; // true, starting with ES5
Specifications
Browser compatibility
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
| toString | 1 | 12 | 1 | 4 | 5 | 1 | 1 | 18 | 4 | 10.1 | 1 | 1.0 | 
| escaping | 73 | 12 | 38 | 9 | 60 | 6 | 73 | 73 | 38 | 52 | 6 | 11.0 | 
See also
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    https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/toString