Example 5

Example 5: Memory and V8 hidden classes

If the compiler can use hidden classes (https://developers.google.com/v8/design), your code will execute MUCH faster and will use MUCH LESS memory.

1. Create some objects
2. Take heap snapshot
3. Compare memory usage

Create objects

Do some calculus

With inner classes	With slow objects

---

'use strict';

var fastObjects = [],
    slowObjects = [];
    
    
function calculateTotalFast(purchase) {
    purchase.total = purchase.units * purchase.price;
}

function calculateTotalSlow(purchase) {
    purchase.total = purchase.units * purchase.price;
}

function slowPurchase(units, price) {
    var slowObject = new SlowPurchase(units, price);
    delete slowObject.x;
    return slowObject;
}

function SlowPurchase(units, price) {
    this.units = units;
    this.price = price;
    this.total = 0;
    this.x = 1;
}

function FastPurchase(units, price) {
    this.units = units;
    this.price = price;
    this.total = 0;
    this.x = 1;
}

function createObjects() {
    var i;
    for (i = 0; i < 300000; i++) {
        fastObjects.push(new FastPurchase(i, 10));
        slowObjects.push(slowPurchase(i, 10));
    }
}


function calculate() {
    var fastStart, slowStart, fastEnd, slowEnd;
    fastStart = new Date();
    fastObjects.forEach(calculateTotalFast);
    fastEnd = new Date();
    slowStart = new Date();
    slowObjects.forEach(calculateTotalSlow);
    slowEnd = new Date();
    document.getElementById("innerTime").innerHTML = fastEnd - fastStart;
    document.getElementById("slowTime").innerHTML  = slowEnd - slowStart;
}