push2.js

function MyArray(arr) {
    const _arr = arr || [];

    this.push = function push(value) {
        console.log('prepush');
        _arr.push(value)
        console.log('postpush');
    }

    this.get = function getByIndex(index) {
        return _arr[index];
    }
}

var arr = new MyArray();
arr.push('5');
console.log(arr.get(0));