19 guidelines for writing efficient jquery code_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 novice, I recommend you read "24 Best Practices for JavaScript Beginners". This is a high-quality JavaScript tutorial. It is best to read it before contacting jQuery.
When you are ready to use jQuery, I strongly recommend that you follow these guidelines:
1. Caching 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);

// Suggestions

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

2 .Avoid Global Variables
With jQuery and 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);

// Suggestions

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

3. Use the Hungarian nomenclature
to prefix the variable with $ to easily identify the jQuery object.

Copy code The code is as follows:

// Oops

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

// 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 similar click() Such a function. In previous versions on() was bind(). Since jQuery version 1.7, on() is the preferred method of 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');
})

// Recommendation
$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');
});

// Suggestions

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

7. Chain operation
It is very easy for jQuery to implement chain operation of methods. 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);

// Suggestions

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

8. Maintain the readability of the code
Along with streamlining the code and using chaining, it may make the code 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);

// Suggestions

$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 && ( Logical AND) or || (Logical OR) operator.

Copy code The code is as follows:

// Oops

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

// Suggestions

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

10. Choose one of the shortcuts
to simplify the code One way is to take advantage of coding shortcuts.

Copy code The code is as follows:

// Oops

if(collection.length > 0){..}

// Suggestions

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 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

// better

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

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

$container.append($element);

12. Memorize skills
You may lack experience in using methods in jQuery, be sure to check 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);

// Suggestions (efficient)

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

13. Cache parent elements 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');

// Suggestions (efficient)

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

14. Avoid universal selectors
Putting universal selectors into descendant selectors has very poor performance.

Copy code The code is as follows:

// Oops

$('.container > *');

// Suggestions

$('.container').children();
Avoid implicit universal selectors
Universal selectors are sometimes implicit and difficult to find.

// Oops

$('.someclass :radio');

// Suggestions

$('.someclass input:radio');
Optimize selectors
For example, the Id selector should be unique, so there is no need to add additional selectors.

// Oops

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

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

15. Avoid multiple ID selectors
emphasize here , 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');

// Suggestions

$('#inner');

16. Stick to the latest version
Newer 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 IE 6/7/8.

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');
});

// Suggestion
$('#stuff').on('click', function() {
console.log('hooray');
});

// Note: This may be inappropriate. Live can achieve real-time binding, and delegate may be more appropriate
17. Use CDN
Google's CND can ensure 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).

18. 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 not be as readable and maintainable as 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). Remember that no framework can be smaller, lighter, and more efficient than native code

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

19. Final advice
Finally, the purpose of recording this article is to improve 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 customized version of jQuery would be a better choice.