JS: RegExp.prototype.test

regex.test(string)

Return true if regex match part or whole of string, else false.

// example of RegExp “test” method
// check if a string match

const gx = RegExp ("4");

console.log ( gx.test ("345")); // true
console.log ( gx.test ("999")); // false

Reference

ECMAScript® 2016 Language Specification#sec-regexp.prototype.test