Optimisation du code source de l'application est un travail très important de grosses applications. langage de programmation JavaScript, Ce problème devient plus important; par applications JavaScript et les applications Web, en particulier les applications Web 2.0 sont toujours limitées par les performances, la capacité des transformateurs et des navigateurs. applications web rendre les navigateurs prennent moins de ressources pour traiter, faire de la vitesse de réponse à l'action de l'utilisateur plus rapide. JavaScript article tutoriel vient autour de la conseils et astuces pour JavaScript jQuery codes.

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#6 – Use ID as Selector whenever possible

Selecting DOM elements using the class attribute is simpler than ever using jQuery. Even though it is simple it should be avoided whenever possible as as selecting using ID is much faster (In IE the class selector seams to loop through the entire DOM why generally it should be avoided). Selecting elements using IDs is fast because the browsers have the native getElementByID method that jQuery will use for IDs. Selecting classes still requires the DOM to be traversed behind the scene and if it is a large DOM and you make several lookups the performance impact can be significant. Let take a look at this simple html code:

<div id="main">

<form method="post" action="/">
  <h2>Selectors in jQuery</h2>

  ...
  ...
  <input class="button" id="main_button" type="submit" value="Submit" />

</form>
</div>
 
...
//Selecting the submit button using the class attribute
//like this is much slower than...
var main_button = $('#main .button');

 
//Selecting the submit button directly using the id like this
var main_button = $('#main_button');

#7 – Use Tags Before Classes

When you are selecting through tags jQuery will use the native browser JavaScript method, getElementsByTagName(). ID is still faster but this is still much faster than selecting with a class name.

<ul id="shopping_cart_items">
  <li><input class="in_stock" name="item" type="radio" value="Item-X" /> Item X</li>

  <li><input class="3-5_days" name="item" type="radio" value="Item-Y" /> Item Y</li>

  <li><input class="unknown" name="item" type="radio" value="Item-Z" /> Item Z</li>

</ul>

It is important to prefix a class with a tag name (here this is “input”) and then it is important to descend from an ID to limit the scope of the selection:

var in_stock = $('#shopping_cart_items input.in_stock');

#8 – Cache jQuery Objects

Caching an object before working with it is essential for performance. You should neverdo like this:

<li>Description: <input type="text" name="description" value="" /></li>

...
$('#shopping_cart_items input.text').css('border', '3px dashed yellow');
$('#shopping_cart_items input.text').css('background-color', 'red');

$('#shopping_cart_items input.text').val("text updated");

In stead cache the object and work on it. The example below should really use chaining but it is just for illustration.

var input_text = $('#shopping_cart_items input.text');

input_text.css('border', '3px dashed yellow');
input_text.css('background-color', 'red');
input_text.val("text updated");

 
//same with chaining:
var input_text = $('#shopping_cart_items input.text');
input_text
 .css('border', '3px dashed yellow')

 .css('background-color', 'red')
 .val("text updated");

#9 – Bind certain jQuery functions to $(window).load event

Most jQuery code examples and tutorials instruct us to bind our jQuery code to the $(document).ready event. In many cases this is OK but since $(document).ready occurs during page render while objects are still downloading it may cause problems for some types of scripts. Functionality such as binding visual effects and animations, drag and drop, pre-fetching hidden images etc. could benefit from being bound to the $(window).load as it will ensure that all dependant elements are ready for use.

$(window).load(function(){
 // Put your jQuery functions that should only initialize after the page has loaded.
});

#10 – Use Chaining to limit selectors, make the code more simple and elegant

Because JavaScript supports chaining and because it works across line breaks you can structure your code like this. This example first removes a class on an element and then adds another to the same element.

$('#shopping_cart_items input.in_stock')
    .removeClass('in_stock')
    .addClass('3-5_days');

If needed it is really simple and useful as well to create a jQuery function that support chaining.

$.fn.makeNotInStock = function() {
    return $(this).removeClass('in_stock').addClass('3-5_days');

}
 
$('#shopping_cart_items input.in_stock').makeNotInStock().log();

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