push3.js

function spyFactory(array) {
    const interceptor = {
        get: function (obj, prop) {
            if (prop !== 'push') { return obj[prop]; }
            
            return function(...args) {
                console.log('prepush');
                Array.prototype.push.apply(this, args);
                console.log('postpush');
            }
        }
    }

    return new Proxy(array, interceptor);
}

const spyedArray = spyFactory([77, 5]);
console.log(spyedArray[0]);
spyedArray.push('4');
console.log(spyedArray[2]);