JSFiddle - React, Tailwind, and code Playground

JavaScript

Array = function() {
    alert('I\'m Hijacked!  Oh no');
};
//Sorry, D.B. says you can't modify any code above this point.

/**
 * Add this as a function on the built-in Array object!
 */
var coolCustomFunction = function() {
    alert('I have ' + this.length + ' elements!  Cool!');
};

Array.prototype.coolCustomFunction = coolCustomFunction;//Modifies hijacked array, not original array.  This makes D.B. sad :(


//Your code to add coolCustomFunction to the original Array object here!



//Your very own D.B.-approved unit test:
var testCoolCustomFunction = function() {
    try {
        var myArray2 = new Array();
        myArray2.coolCustomFunction();
    } catch (e) {
        alert('Fail!');
    }
};
testCoolCustomFunction();