Summary of writing techniques to improve jQuery code efficiency

Cache variables

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

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

Avoid global variables

JQuery is the same as JavaScript, in general, it’s best to make sure your variables are within function scope.

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

Use Hungarian nomenclature

Add $ prefix before the variable to easily identify the jQuery object.

// 糟糕var first = $('#first');var second = $('#second');var value = $first.val();// 建议 - 在jQuery对象前加$前缀var $first = $('#first');var $second = $('#second'),var value = $first.val();

Use Var chain (single Var mode)

Combine multiple var statements into one statement. I recommend putting unassigned variables at the end.

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

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 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.

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

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

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

Streamline javascript

Generally speaking, it is best to combine functions as much as possible.

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

Chain operation

It is very easy to implement chain operation of methods in jQuery. Take advantage of this below.

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

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.

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

Select short-circuit evaluation

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

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

Choose shortcuts

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

// 糟糕if(collection.length > 0){..}// 建议if(collection.length){..}

Separating 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 separate the elements first and then Adding.

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

$element = $containerLi.first();//... 许多复杂的操作// bettervar$container = $("#container"),
    $containerLi = $container.find("li"),
    $element = null;

$element = $containerLi.first().detach();//... 许多复杂的操作$container.append($element);

Memory Tips

You may lack experience in using methods in jQuery, be sure to check the documentation, there may be a better or faster method to use it.

// 糟糕$('#id').data(key,value);// 建议 (高效)$.data('#id',key,value);

Using subqueries to cache parent elements

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.

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

Avoid universal selectors

Putting universal selectors into descendant selectors has very poor performance.

// 糟糕$('.container > *');// 建议$('.container').children();

Avoid implicit universal selectors

Universal selectors are sometimes implicit and difficult to detect.

// 糟糕$('.someclass :radio');// 建议$('.someclass input:radio');

Optimize selectors

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

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

Avoid multiple ID selectors

I emphasize that the ID selector should be unique, there is no need to add additional selectors, and there is no need for multiple Descendant ID selector.

// 糟糕$('#outer #inner');// 建议$('#inner');

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 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.

// 糟糕 - live 已经废弃$('#stuff').live('click', function() {
  console.log('hooray');
});// 建议$('#stuff').on('click', function() {
  console.log('hooray');
});// 注：此处可能不当，应为live能实现实时绑定，delegate或许更合适

Using 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).

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). 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 strongly recommend absorbing the best of both worlds and using (if possible) native code equivalent to jQuery.

jQuery writing principles:

1. Don’t overuse jQuery

1. No matter how fast jQuery is, it cannot be compared with the native javascript method, and the jQuery created Objects contain a huge amount of information. Therefore, when there are native methods that can be used, try to avoid using jQuery.

2. Many jQuery methods have two versions, one for jQuery objects and another for jQuery functions. Since the latter does not operate through jQuery objects, it has relatively less overhead and is faster.

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