How to use jquery efficiently-JS Tutorial-php.cn

As a programmer, you will definitely use jQuery and javascript. So if we want to develop a good program, how can we use jQuery and javascript more efficiently to improve your jQuery and javascript code? Good code will bring speed improvements, and fast rendering and response mean a better user experience. So the content of this section is to bring you the efficient use of jQuery and javascript.

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 JavaScript Best Practices for 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. Cache variables

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

//糟糕h=$(&#39;#element&#39;).height();$(&#39;#element&#39;).css(&#39;height&#39;,h-20);
//建议$element=$(&#39;#element&#39;);h=$element.height();$element.css(&#39;height&#39;,h-20);

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2. Avoid global variables

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

//糟糕$element=$(&#39;#element&#39;);h=$element.height();$element.css(&#39;height&#39;,h-20);
//建议var $element=$(&#39;#element&#39;);var h=$element.height();$element.css(&#39;height&#39;,h-20);

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3. Use Hungarian nomenclature

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

//糟糕
var first=$(&#39;#first&#39;);
var second=$(&#39;#second&#39;);
var value=$first.val();

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// 建议 - 在 jQuery 对象前加 $ 前缀    
var $first=$(&#39;#first&#39;);
var $second=$(&#39;#second&#39;),
var value=$first.val();

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4. Use var chain (single var mode)

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

var 
  $first=$(&#39;#first&#39;),
  $second=$(&#39;#second&#39;),
  value=$first.val(),
  k=3,
  cookiestring=&#39;SOMECOOKIESPLEASE&#39;,
  i,
  j,
  myArray={};

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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.

//糟糕$first.click(function(){    $first.css(&#39;border&#39;,&#39;1px solid red&#39;);    $first.css(&#39;color&#39;,&#39;blue&#39;);});
$first.hover(function(){    $first.css(&#39;border&#39;,&#39;1px solid red&#39;);})
// 建议$first.on(&#39;click&#39;,function(){    $first.css(&#39;border&#39;,&#39;1px solid red&#39;);    $first.css(&#39;color&#39;,&#39;blue&#39;);})
$first.on(&#39;hover&#39;,function(){    $first.css(&#39;border&#39;,&#39;1px solid red&#39;);})

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6. Simplify javascript

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

//糟糕$first.click(function(){    $first.css(&#39;border&#39;,&#39;1px solid red&#39;);    $first.css(&#39;color&#39;,&#39;blue&#39;);});
//建议$first.on(&#39;click&#39;,function(){    $first.css({        &#39;border&#39;:&#39;1px solid red&#39;,        &#39;color&#39;:&#39;blue&#39;    });});

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7. Chained operations

jQuery It is very easy to implement chained operations of methods. Take advantage of this below.

//糟糕$second.html(value);$second.on(&#39;click&#39;,function()
{    alert(&#39;hello everybody&#39;);});$second.fadeIn(&#39;slow&#39;);$second.animate({height:&#39;120px&#39;},500);
//建议$second.html(value);$second.on(&#39;click&#39;,function()
{    alert(&#39;hello everybody&#39;);}).fadeIn(&#39;slow&#39;).animate({height:&#39;120px&#39;},500);

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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.

//糟糕$second.html(value);$second.on(&#39;click&#39;,function()
{    alert(&#39;hello everybody&#39;);}).fadeIn(&#39;slow&#39;).animate({height:&#39;120px&#39;},500);
//建议$second.html(value);$second    .on(&#39;click&#39;,function(){ alert(&#39;hello everybody&#39;);})    .fadeIn(&#39;slow&#39;)    .animate({height:&#39;120px&#39;},500);

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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.

//糟糕function initVar($myVar) {    if(!$myVar) {        $myVar=$(&#39;#selector&#39;);    }}
//建议function initVar($myVar) {    $myVar=$myVar || $(&#39;#selector&#39;);}

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10. 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){..}

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

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12. Memorize Tips

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

//糟糕$(&#39;#id&#39;).data(key,value);
// 建议 (高效)  $.data(&#39;#id&#39;,key,value);

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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.

//糟糕var     $container=$(&#39;#container&#39;),    $containerLi=$(&#39;#container li&#39;),    $containerLiSpan=$(&#39;#container li span&#39;);
// 建议 (高效)  var     $container=$(&#39;#container &#39;),    $containerLi=$container.find(&#39;li&#39;),    $containerLiSpan= $containerLi.find(&#39;span&#39;);

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14. Avoid universal selectors

Putting universal selectors into descendant selectors has very poor performance.

//糟糕$(&#39;.container > *&#39;);
//建议$(&#39;.container&#39;).children();

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15. Avoid implicit universal selectors

Universal selectors are sometimes implicit and difficult to find.

//糟糕$(&#39;.someclass :radio&#39;);
//建议$(&#39;.someclass input:radio&#39;);

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16. Optimize selectors

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

//糟糕$(&#39;div#myid&#39;); $(&#39;div#footer a.myLink&#39;);
// 建议$(&#39;#myid&#39;);$(&#39;#footer .myLink&#39;);

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17. Avoid multiple ID selectors

I emphasize here 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$(&#39;#outer #inner&#39;);
//建议$(&#39;#inner&#39;);

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18. Stick to the latest version

Newer versions are usually better: lighter weight, 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 the deprecated methods in each new version and try to avoid using these methods.

//糟糕- live 已经废弃   $(&#39;#stuff&#39;).live(&#39;click&#39;,function() {  console.log(&#39;hooray&#39;);});
// 建议$(&#39;#stuff&#39;).on(&#39;click&#39;,function() {  console.log(&#39;hooray&#39;);});
// 注：此处可能不当，应为live能实现实时绑定，delegate或许更合适

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20. 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).

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

The purpose of 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 custom version of jQuery would be a better choice.

The above is how to use jQuery and javascript efficiently. After reading this article, I hope it will be helpful to everyone's development.

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