Tips for writing better jQuery code

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 "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:

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

With jQuery, like 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 variables to easily identify jQuery objects.

// 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 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.

/

/ 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

In general, it’s best to combine functions whenever 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'
 });
});

Chained operations

It is very easy to implement chained operations 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.

// 糟糕
$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 the && (logical AND) or || (logical OR) operators.

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

Choose shortcuts

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

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

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 separate the elements first and then add them.

// 糟糕
var
 $container = $("#container"),
 $containerLi = $("#container li"),
 $element = null;
$element = $containerLi.first(); 
//... 许多复杂的操作
// better
var
 $container = $("#container"),
 $containerLi = $container.find("li"),
 $element = null;
$element = $containerLi.first().detach(); 
//... 许多复杂的操作
$container.append($element);

Know the tips

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.

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

Cache parent element using subquery

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 terrible performance.

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

Avoid implicit universal selectors

Universal selectors are sometimes implicit and not easy to spot.

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

Optimized 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 would like to 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 selectors.

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

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.

Discard 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.