JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = ["one","two","three"];

Array.prototype.find = function(val){
    for(var i = 0; i < this.length; i++) {
        if(this[i] === val){
            alert("found");
            return;
        }
    }
    alert("not found");
}

arr.find("two");