Create a fixed length array

demo.js

let arr = [];
arr.maxLength = 3;

Array.prototype.pushLimited = function(elem) {
    if (this.length === this.maxLength) {
        throw new Error('max length exceeded');
    } else {
        this.push(elem);
    }
}

arr.pushLimited('A');
arr.pushLimited('B');
arr.pushLimited('C');
arr.pushLimited('D');
arr.pushLimited('E');

console.log(arr);