JSFiddle - React, Tailwind, and code Playground

by Khalil Zhang

JavaScript

Array.prototype.duplicate = function () {
    // modify the original array
    Array.prototype.push.apply(this, this);
}

Array.prototype.duplicateWithConcat = function () {
    // Not modify the original array
    return this.concat(this);
}


var arr = [1, 2, 3];
arr.duplicate();
console.dir(arr);


var arr = [1, 2, 3];
console.dir(arr.duplicateWithConcat());