array.push

var numbers = [1, 2, 3];
numbers.push(4

console.log(numbers // [1, 2, 3, 4]

numbers.push(5, 6, 7

console.log(numbers // [1, 2, 3, 4, 5, 6, 7]

arr.push([element1[, ...[, elementN]]])

var sports = ['soccer', 'baseball'];
var total = sports.push('football', 'swimming'

console.log(sports // ['soccer', 'baseball', 'football', 'swimming']
console.log(total  // 4

var vegetables = ['parsnip', 'potato'];
var moreVegs = ['celery', 'beetroot'];

// Merge the second array into the first one
// Equivalent to vegetables.push('celery', 'beetroot'
Array.prototype.push.apply(vegetables, moreVegs

console.log(vegetables // ['parsnip', 'potato', 'celery', 'beetroot']

var obj = {
    length: 0,

    addElem: function addElem(elem) {
        // obj.length is automatically incremented 
        // every time an element is added.
        [].push.call(this, elem
    }
};

// Let's add some empty objects just to illustrate.
obj.addElem{}
obj.addElem{}
console.log(obj.length
// → 2