JSFiddle - React, Tailwind, and code Playground

by Peer Reynders

JavaScript

const a = ['1', '2', '3'];
const i = 5;
a[i] = '4';

console.log(a); // (6) [ "1", "2", "3", empty x 2, "4" ]
                // Array(6) [ "1", "2", "3", <2 empty slots>, "4" ]
a[i-1] = undefined;
console.log(a); // (6) [ "1", "2", "3", empty, undefined, "4" ]
                // Array(6) [ "1", "2", "3", <1 empty slot>, undefined, "4" ]

console.log(a.hasOwnProperty(i-2)); // false 
console.log(a.hasOwnProperty(i-1)); // true