JSFiddle - React, Tailwind, and code Playground

by alirokni

JavaScript

Array.prototype.duplicate = function() {
    this.push.apply(this, this);
    return this;
}
alert([1,2,3,4,5].duplicate());

Array.prototype.duplicate = function() {
    return this.concat(this);
}

console.log([1,2,3,4,5].duplicate());