JSFiddle - React, Tailwind, and code Playground

HTML

<button onclick="regexTest()">Test</button>

JavaScript

function regexTest() {
    var regexp;
    var lit;
     // Lookahead
    var regexp = new RegExp("^(?=.*[a-z]).+$","g");
    var lit = /^(?=.*[a-z]).+$/g;
    alert("abd = ^(?=.*[a-z]).+$ : RegExp= " + regexp.test("abc") + " : Lit= " + lit.test("abc"));
    // Lookahead - Digit
    var regexp = new RegExp("^(?=.*\d).+$","g");
    var lit = /^(?=.*\d).+$/g;
    alert("1 = ^(?=.*\d).+$ : RegExp= " + regexp.test("1") + " : Lit= " + lit.test("1"));    

    // Backref
    var regexp = new RegExp("^(.)\1$","g");
    var lit = /^(.)\1$/g;
    alert("aa = ^(.)\1$ : RegExp= " + regexp.test("aa") + " : Lit= " + lit.test("aa"));
    
    // Negitive lookahead
    var regexp = new RegExp("^(?!.*\d).+$","g");
    var lit = /^(?!.*\d).+$/g;
    alert("abc123 = ^(?!.*\d).+$ : RegExp= " + regexp.test("abc123") + " : Lit= " + lit.test("abc123"));    
        
}