Symbol.match

The Symbol.match well-known symbol specifies the matching of a regular expression against a string. This function is called by the String.prototype.match() method.

This function is also used to identify if objects have the behavior of regular expressions. For example, the methods String.prototype.startsWith(), String.prototype.endsWith() and String.prototype.includes(), check if their first argument is a regular expression and will throw a TypeError if they are. Now, if the match symbol is set to false (or a Falsy value), it indicates that the object is not intended to be used as a regular expression object.

The following code will throw a TypeError:

'/bar/'.startsWith(/bar/);

// Throws TypeError, as /bar/ is a regular expression
// and Symbol.match is not modified.

However, if you set Symbol.match to false, the isRegExp check (that uses the match property) will indicate that the object is not a regular expression object. The methods startsWith and endsWith won't throw a TypeError as a consequence.

var re = /foo/;
re[Symbol.match] = false;
'/foo/'.startsWith(re); // true
'/baz/'.endsWith(re);   // false

• Polyfill of Symbol.match in core-js
• Symbol.replace
• Symbol.search
• Symbol.split
• RegExp.prototype[@@match]()