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# Tuesday, July 30, 2013

What is the slowest function in kendo? Or better, which function has most negative performance impact in kendo.

Recently, we were dealing with a simple page, which was too slow, as data binding took more than second.

The page contained a dropdown list, with ~1000 options. To understand the reason we have run this page under the IE's built-in javascript profiler, and ...

there, we have found that almost half of the time is taken by a function (call it X), which receives nothing and returns always the same result!

But, let's now see a minimal example that demostrates the problem:

<!DOCTYPE html>
    <script src="scripts/jquery/jquery.js"></script>
    <script src="scripts/kendo/kendo.web.min.js"></script>
    <link href="styles/kendo.common.min.css" rel="stylesheet" />
    <link href="styles/kendo.default.min.css" rel="stylesheet" />
    <link href="styles/style.css" rel="stylesheet" />
var model;

function init()
  var source = [];

  for(var i = 0; i < 1000; ++i)
    source.push({ text: "value " + i, value: "" + i });

  model = kendo.observable(
    value: "1",
    source: new
      data: source

function test()
  kendo.bind("#view", model);

  <button onclick="test()">Click to start test</button>
<p id="view">
  <input data-role="dropdownlist"
    data-bind="value: value, source: source"

There are two parts: initialization, and a test itself that starts upon button click.

In the initialization part we have defined a model, containing a datasource.

The test part performs data binding.

Now, here is a run statistics:

Function Count Inclusive time (ms) Inclusive time % Avg time (ms)
test 1 456.05 100 456.05
X 1,000 200.14 43.89 0.2

So, X is fast by itself, but it run 1000 times, and took about 44% of all time.

And now, to the function. It's

Here is its code:

_ns: function(ns) {
  ns = ns || kendo.ui;
  var all = [ kendo.ui, kendo.dataviz.ui, ];
  all.splice($.inArray(ns, all), 1);

  return kendo.rolesFromNamespaces(all);

We can see that on each call it receives a parameter undefined, and always returns an array with the same content. Not sure why Kendo UI team made it so complex, but one can easily device a simple patch that optimizes this code path.

function patch()
  var base =;
  var result; = function(ns)
    return ns ?, ns) :
      (result || (result =, ns)));

With this patch applied, the profiler shows:

Function Count Inclusive time (ms) Inclusive time % Avg time (ms)
test 1 253.03 100 253.03
_ns 1,000 6 2.37 0.01

Execution time dropped considerably, and _ns() loses its title of most time consuming function!

An example can be found at slow.html.

Tuesday, July 30, 2013 8:47:11 PM UTC  #    Comments [0] -
javascript | kendoui
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