Symbol.match

The well-known symbol Symbol.match.

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 except undefined), 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 object will be considered as not a regular expression object. The methods startsWith and endsWith won't throw a TypeError as a consequence.

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

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