JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = [];
console.log(arr.length); //Output: 0

arr["1231321"] = "abcd";
console.log(arr.length); //Output: 1231322
arr = [];
arr["1231321".toString()] = "abcd";
console.log(arr.length); //Output: 1231322
arr = [];
arr["a1231321"] = "abcd";
console.log(arr.length); //Output: 0
arr = [];
arr["1231321a"] = "abcd";
console.log(arr.length); //Output: 0