22 suggestions on jquery performance optimization_jquery

First of all, keep in mind that jQuery is javascript. This means we should adopt the same coding conventions, style guides and best practices.

First of all, if you are a javascript newbie, I recommend you read "24 JavaScript Best Practices for Beginners". This is a high-quality javascript tutorial. It is best to read it before getting into jQuery.

When you are ready to use jQuery, I strongly recommend that you follow these guidelines:

1. Cache variables

DOM traversal is expensive, so try to cache reused elements.

Copy code The code is as follows:

//Oops
h=$('# element').height();
$('#element').css('height',h-20);

Copy code The code is as follows:

//Suggestion
$element=$(' #element');
h=$element.height();
$element.css('height',h-20);

2. Avoid global variables

jQuery As with javascript, in general it's best to make sure your variables are within function scope.

Copy code The code is as follows:

//Oops
$element=$(' #element');
h=$element.height();
$element.css('height',h-20);

Copy code The code is as follows:

//Suggestion
var $element=$( '#element');
var h=$element.height();
$element.css('height',h-20);

3. Use Hungarian nomenclature

Add $ prefix before variables to easily identify jQuery objects.

Copy code The code is as follows:

//Oops
var first=$(' #first');
var second=$('#second');
var value=$first.val();

Copy code The code is as follows:

// Suggestion - Prefix the jQuery object with $
var $first=$('#first');
var $second=$('#second'),
var value=$first.val();

4. Use var chain (single var mode)

To combine multiple var statements into one statement, I recommend putting unassigned variables at the end.

Copy code The code is as follows:

var
$first=$('#first '),
$second=$('#second'),
value=$first.val(),
k=3,
cookiestring='SOMECOOKIESPLEASE',
i,
j,
myArray={};

5. Please use 'on'

In the new version of jQuery, the shorter on("click") is used to replace functions like click(). In previous versions on() was bind(). Since jQuery 1.7, on() is the preferred method for attaching event handlers. However, for consistency's sake, you can simply use the on() method all together.

Copy code The code is as follows:

//Oops
$first.click(function (){
$first.css('border','1px solid red');
$first.css('color','blue');
});

$first.hover(function(){
$first.css('border','1px solid red');
})

Copy code The code is as follows:

// Suggestion
$first.on(' click',function(){
$first.css('border','1px solid red');
$first.css('color','blue');
})

$first.on('hover',function(){
$first.css('border','1px solid red');
})

6. Simplify javascript

In general, it’s best to combine functions whenever possible.

Copy code The code is as follows:

//Oops
$first.click(function (){
$first.css('border','1px solid red');
$first.css('color','blue');
});

Copy code The code is as follows:

//Suggestion
$first.on(' click',function(){
$first.css({
'border':'1px solid red',
'color':'blue'
});
}) ;

7. Chain operation

It is very easy to implement method chaining operations in jQuery. Take advantage of this below.

Copy code The code is as follows:

//Oops
$second.html(value );
$second.on('click',function(){
alert('hello everybody');
});
$second.fadeIn('slow');
$second.animate({height:'120px'},500);

Copy code The code is as follows:

//Suggestion
$second.html(value );
$second.on('click',function(){
alert('hello everybody');
}).fadeIn('slow').animate({height:'120px' },500);

8. Maintain code readability

Along with streamlining the code and using chaining, the code may become difficult to read. Adding pinches and line breaks can work wonders.

Copy code The code is as follows:

//Oops
$second.html(value );
$second.on('click',function(){
alert('hello everybody');
}).fadeIn('slow').animate({height:'120px' },500);

Copy code The code is as follows:

//Suggestion
$second.html(value );
$second
.on('click',function(){ alert('hello everybody');})
.fadeIn('slow')
.animate({height: '120px'},500);

9. Select short-circuit evaluation

Short-circuit evaluation is an expression that is evaluated from left to right, using the && (logical AND) or || (logical OR) operators.

Copy code The code is as follows:

//Oops
function initVar($myVar) {
if(!$myVar) {
$myVar=$('#selector');
}
}

Copy code The code is as follows:

//Suggestion
function initVar($myVar) {
$myVar=$myVar || $('#selector');
}

10. Select shortcut

One way to streamline your code is to take advantage of coding shortcuts.

[code]
//Oops
if(collection.length > 0){..}

Copy code The code is as follows:

//Suggestion
if(collection.length) {..}

11. Separate elements during heavy operations

If you plan to do a lot of operations on DOM elements (setting multiple attributes or css styles in succession), it is recommended to detach the elements first and then add them.

Copy code The code is as follows:

//Oops
var
$container=$("#container"),
$containerLi=$("#container li"),
$element=null;

$element=$containerLi.first();
//... Many complex operations

Copy code The code is as follows:

//Suggestion
var
$container =$("#container"),
$containerLi=$container.find("li"),
$element=null;

$element=$containerLi.first().detach();
//... Many complex operations

$container.append($element);

12. Memorize skills

You may be inexperienced with using methods in jQuery, be sure to check out the documentation, there may be a better or faster way to use it.

Copy code The code is as follows:

//Oops
$('#id' ).data(key,value);

Copy code The code is as follows:

// Suggestion (efficient)
$.data ('#id',key,value);

13. Parent elements cached using subqueries

As mentioned earlier, DOM traversal is an expensive operation. A typical approach is to cache parent elements and reuse these cached elements when selecting child elements.

Copy code The code is as follows:

//Oops
var
$container =$('#container'),
$containerLi=$('#container li'),
$containerLiSpan=$('#container li span');

Copy code The code is as follows:

// Suggestion (efficient)
var
$container=$('#container '),
$containerLi=$container.find('li'),
$containerLiSpan= $containerLi.find('span');

14. Avoid universal selectors

Putting the universal selector into a descendant selector has terrible performance.

Copy code The code is as follows:

//Oops
$('.container > ; *');

Copy code The code is as follows:

//Suggestion
$('.container' ).children();

15. Avoid implicit universal selectors

Universal selectors are sometimes implicit and difficult to find.

Copy code The code is as follows:

//Oops
$('.someclass: radio');

Copy code The code is as follows:

//Suggestion
$('.someclass input :radio');

16. Optimization selector

For example, the id selector should be unique, so there is no need to add additional selectors.

Copy code The code is as follows:

//Oops
$('div#myid ');
$('div#footer a.myLink');

Copy code The code is as follows:

// Suggestion
$('#myid' );
$('#footer .myLink');

17. Avoid multiple ID selectors

It is emphasized that the ID selector should be unique, there is no need to add additional selectors, and there is no need for multiple descendant ID selectors.

Copy code The code is as follows:

//Oops
$('#outer # inner');

Copy code The code is as follows:

//Suggestion
$('#inner' );

18. Stick to the latest version

New versions are usually better: more lightweight and more efficient. Obviously, you need to consider the compatibility of the code you want to support. For example, version 2.0 does not support Internet Explorer 6/7/8.

19. Abandon deprecated methods

It is very important to pay attention to deprecated methods with each new version and try to avoid using these methods.

Copy code The code is as follows:

//Oops - live has been abandoned
$( '#stuff').live('click',function() {
console.log('hooray');
});

Copy code The code is as follows:

// Suggestion
$('#stuff' ).on('click',function() {
console.log('hooray');
});
// Note: This may be inappropriate, it should be that live can achieve real-time binding , delegate may be more appropriate

20. Utilize CDN

Google’s CND ensures that the cache closest to the user is selected and responds quickly. (Please search the address yourself when using Google CND. The address here cannot be used. We recommend the CDN provided by jquery official website).

21. Combine jQuery and javascript native code when necessary

As mentioned above, jQuery is javascript, which means that anything you can do with jQuery can also be done with native code. Native code (or vanilla) may be less readable and maintainable than jQuery, and the code is longer. But it also means more efficient (usually the closer to the underlying code the less readable the higher the performance, for example: assembly, which of course requires more powerful people). Keep in mind that no framework can be smaller, lighter, and more efficient than native code (note: the test link is no longer valid, you can search for the test code online).

Given the performance differences between vanilla and jQuery, I highly recommend taking the best of both and using (if possible) native code equivalent to jQuery.

22. Final advice

Finally, I recorded this article with the purpose of improving the performance of jQuery and some other good suggestions. If you want to delve deeper into this topic you will find a lot of fun. Remember, jQuery is not required, just an option. Think about why you want to use it. DOM manipulation? ajax? stencil? css animation? Or a selector engine? Perhaps a javascript microframework or a custom version of jQuery would be a better choice.