Periksa apakah elemen ada di JS
//includes
const fruits = ["apple", "mango", "banana", "kiwi"]
return fruits.includes("mango") ? true : false; //returns true if element is in the array
//find Index
let matchIndex = fruits.findIndex((fruit)=>{return fruit == "mango"});
matchIndex > -1 ? fruits[matchIndex] : null;
//other than -1 means the element is in the array.
JS Ninja