javascript static data property
Symbol.match
The Symbol.match static data property represents the well-known symbol Symbol.match. The match() method looks up this symbol on its first argument for the method used to match an input string against the current object. This symbol is also used to determine if an object should be treated as a regex.
For more information, see RegExp.prototype[Symbol.match]() and match().
const regexp = /foo/;
// console.log('/foo/'.startsWith(regexp));
// Expected output (Chrome): Error: First argument to String.prototype.startsWith must not be a regular expression
// Expected output (Firefox): Error: Invalid type: first can't be a Regular Expression
// Expected output (Safari): Error: Argument to String.prototype.startsWith cannot be a RegExp
regexp[Symbol.match] = false;
console.log("/foo/".startsWith(regexp));
// Expected output: true
console.log("/baz/".endsWith(regexp));
// Expected output: false
Value
The well-known symbol Symbol.match.
0
Description
This function is also used to identify if objects have the behavior of regular expressions. For example, the methods startsWith(), endsWith() and 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.
Examples
Marking a RegExp as not a regex
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