JavaScript

This site contains weird, un(der)documented and security-relevant behaviour of JavaScript in general and various standard library functions.

RegExp.prototype.test()

The test() method of RegExp instances executes a search with this regular expression for a match between a regular expression and a specified string. Returns true if there is a match; false otherwise.

– From mdn.

When passed a non-string value, the given value will first be transformed to a string by its type-specific ToString() abstract operation. Take this sample code for instance.

/foo/.test(["foo", "bar", "baz"]);

The given array ["foo", "bar", "baz"] will be transformed to a string like "foo,bar,baz". Thus, the above code is equivalent to /foo/.test("foo,bar,baz");. The test() call will thus return true. This works for any type with a ToString() abstract operation.

See mdn and the spec.