web application profiling using code snippets

Dr. Gleb Bahmutov PhD

Kensho, Boston / NYC

 

 

Kensho app

User: Page is slow to load

Dev: How long does it take to load thE page?

solution 1:

Observe the Network panel

hint: use throttling

Solution 2: use chrome stats object

(function timeFirstPaint() {
  var fp = chrome.loadTimes().firstPaintTime - 
    chrome.loadTimes().startLoadTime;
  console.log('first paint: ' + fp);
}());

Copy / paste this code into the Chrome browser console

Pasting and running the same code over and over

there has got to be a better way

Chrome > DevTools > Sources > Snippets

How long does the page load?

Code Snippets

find Expensive images

Include missing styles

<h1>
    <i class="fa fa-flag"></i> Include missing styles 
    <i class="fa fa-heart"></i>
</h1>
(function addFontAwesomeCssLink() {
  var ss = document.createElement('link');
  ss.type = 'text/css';
  ss.rel = 'stylesheet';
  ss.href = '//maxcdn.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.min.css';
  document.getElementsByTagName("head")[0].appendChild(ss);
}());

user: The app is slow

qa: Why is this action slow?

dev: how long does this javascript function run?

profiling javascript

// "app" code
function add(a, b) {
  return a + b;
}

// "user" code
function onClick() {
  console.log(add(2, 3));
}
// click!
// 5

within 0.1 second ?

time add function

// "app" code
function add(a, b) {
  var started = Number(new Date());
  var sum = a + b;
  var finished = Number(new Date());
  console.log('add took', 
    finished - started, 'ms');
  return sum;
}


// "user" code
function onClick() {
  console.log(add(2, 3));
}
// click!
// add took 10ms
// 5

time a function call via external overwrite

// "app" code
function add(a, b) {
  return a + b;
}


// "user" code
function onClick() {
  var started = Number(new Date());
  console.log(add(2, 3));
  var finished = Number(new Date());
  console.log('add took', 
    finished - started, 'ms');
}
// click!
// 5
// add took 10ms

wrap add from snippet

// "app" code
function add(a, b) {
  return a + b;
}

// "user" code
function onClick() {
  console.log(add(2, 3));
}
// code snippet
function profileAdd() {
  var _add = add;
  add = function profiledAdd(a, b) {
    var started = Number(new Date());
    var sum = _add(a, b);
    var finished = Number(new Date());
    console.log('add took', finished - started, 'ms');  
    return sum;
  };
}

wrap add from snippet might not work

// "app" code
function add(a, b) {
  return a + b;
}

// "user" code
function onClick() {
  var todo = add.bind(null, 2, 3);
  console.log(todo();
}
// code snippet
function profileAdd() {
  var _add = add;
  add = function profiledAdd(a, b) {
    ...
  };
}

Prefer wrapping methods

// "app" code
function add(a, b) {
  return a + b;
}
var calc = {
  add: add
};
// "user code"
function click(calc) {
  console.log(calc.add(2, 3));
}
// code snippet
var _add = calc.add;
calc.add = function () {
  console.log('adding', arguments);
  return _add.apply(calc, arguments);
}
// adding { '0': 2, '1': 3 }
// 5

Works in Angular

var selector = 'load';
var methodName = 'load';
var el = angular.element(document.getElementById(selector));
var scope = el.scope() || el.isolateScope();
var fn = scope[methodName];
var $timeout = el.injector().get('$timeout');
var $q = el.injector().get('$q');

scope[methodName] = function () {
  console.profile(name);
  console.time(name);

  // method can return a value or a promise
  var returned = fn();
  $q.when(returned).finally(function finishedMethod() {
    console.timeStamp('finished', methodName);

    $timeout(function afterDOMUpdate() {
      console.timeStamp('dom updated after', methodName);
      console.timeEnd(name);
      console.profileEnd();
    
      scope[methodName] = fn;
    }, 0);
  });
};

Works with prototypes

// tough cases like jQuery plugins
new Photostack(document.getElementById('photostack-3');
function profile(proto, methodName) {
    var originalMethod = proto[methodName];
    function restoreMethod() {
        console.timeEnd(methodName);
        proto[methodName] = originalMethod;
    } 
    proto[methodName] = function () {
        console.time(methodName);
        originalMethod.apply(this, arguments);
        restoreMethod();
    };
}
// where we want to profile Photostack.prototype._rotate
profile(Photostack.prototype, '_rotate');

js profiling example

my profiling rules

  • Profile in a "clean" browser

  • profile the actual application

  • optimize the top bottleneck first

Warning signs

  • try - catch blocks
  • modifying arguments
    • arguments = arguments || []
  • deleting / adding properties
    • delete foo.bar
  • calling function with different argument types
function add(a, b) {
    return a + b;
}
add(2, 3);
add('foo', 'bar');

Will not be optimized

  • eval
  • debug
  • long functions!

iojs 1.8.1 has more than 300 switches. A lot related to performance tuning

 

            iojs --v8-options
        

bad flame chart

good flame chart

time web worker

var worker = new Worker('worker.js');
function renderPrimes(primes) {
    var html = primes.map(primeToRow).join('\n');
    document.querySelector('#results').innerHTML = html;
}
worker.onmessage = function (e) {
    console.log('worker has finished');
    renderPrimes(e.data);
};
var primesApp = {
    worker: worker,
    findFirstPrimes: function (n) {
        console.log('finding first', n, 'primes');
        worker.postMessage({ cmd: 'primes', n: n });
    }
};
document.querySelector('#find').addEventListener('click', function () {
    var n = Number(document.querySelector('#n').value);
    primesApp.findFirstPrimes(n);
});

Need to time separate actions

var m1 = obj1[methodName1];
var m2 = obj2[methodName2];

obj1[methodName1] = function () {
    console.profile('separate');
    console.time('separate');
    m1.apply(obj1, arguments);
};

obj2[methodName2] = function () {
    console.timeEnd('separate');
    console.profileEnd('separate');
    m2.apply(obj2, arguments);
};

// call with
// obj1 = primesApp.worker, methodName1 = 'postMessage'
// obj2 = primesApp.worker, methodName2 = 'onmessage'  

Solution: wrap 2 steps into a single promise

// "user" code
webWorker.computePrimes(10000)
    .then(render);
// can be wrapped easily in a code snippet
var started = Number(new Date());
var result = webWorker.computePrimes(1000);
if (isPromise(result)) {
  return result.tap(function () {
    var finished = Number(new Date());
  });
} else {
  ... // time normally
}

What about timeline?

Layout profiler

Paint profiler

Weird behavior when trying to start from a code snippet (or browser console)

Observe paint

Can code snippets be updated?

YES, inception-style

Related

MUST watch: "DevTools: State of the Union" by @addyosmani

Q: How much to optimize?

A: Set a budget

  • page load time (text)

  • images appear

  • each click has visual action

  • browser is never locked

Q: How much to optimize?

A: Set a budget

  • page load time (text)

  • images appear

  • each click has visual action

  • browser is never locked

500ms

1000ms

100ms

30FPS

Q: how to stick to the performance budget as web app grows?

still searching for an answer

web application profiling using code snippets

web application profiling using code snippets

By Gleb Bahmutov

web application profiling using code snippets

Chrome DevTools code snippets became my favorite tool when investigating performance bottlenecks in web applications. A JavaScript fragment can be stored as a named snippet in the "Sources" DevTools panel and executed in the current page's context, just as if it were a code executed in the browser's console.

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