Some tips for writing efficient JSLite code imitating JQuery_jquery

It is not uncommon for articles to discuss jQuery and javascript performance. However, I plan to teach you how to improve your JSLite and JavaScript code based on some speed tips and suggestions that others have put together for jQuery. Good code will bring speed improvements. Fast rendering and responsiveness means a better user experience.

First of all, keep in mind that JSLite 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 and have never used jQuery, I suggest you read the syntax introduction of the official document first. This is a high-quality javascript tutorial, which means that you have been using jQuery for a while. .

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

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

Avoid global variables

JSLite is the same as JavaScript. Generally speaking, it is best to ensure that your variables are within function scope.

Copy code The code is as follows:

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

Use Hungarian nomenclature

Add $ prefix before variables to easily identify JSLite objects.

Copy code The code is as follows:

// Oops
var first = $('#first');
var second = $('#second');
var value = $first.val();
// Suggestion - Prefix JSLite objects with $
var $first = $('#first');
var $second = $('#second'),
var value = $first.val();

Use var chain (single var mode)

Consolidate 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 = {};

Please use on

In the new version of JSLite, the shorter on("click") is used to replace functions like click(). In previous versions on() was bind() . 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');
})
// 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');
})

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

Chain operation

It is very easy to implement chained operations of methods in JSLite. 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);
// Suggestion
$second.html(value);
$second.on('click',function(){
alert('hello everybody');
}).fadeIn('slow').animate({height:'120px'},500);

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);
// Suggestion
$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.

Copy code The code is as follows:

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

Select shortcut

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

Copy code The code is as follows:

// Oops
if(collection.length > 0){..}
// Suggestion
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 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);

Memory skills

You may be inexperienced with using methods in JSLite, 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);
// Suggestion (efficient)
$.data('#id',key,value);

Parent element cached 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.

Copy code The code is as follows:

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

Avoid universal selectors

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

Copy code The code is as follows:

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

Avoid implicit universal selectors

Universal selectors are sometimes implicit and difficult to find.

Copy code The code is as follows:

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

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

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.

Copy code The code is as follows:

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

Stick to the latest version

New versions are usually better: more lightweight, more efficient, with more methods, and more comprehensive coverage of jQuery methods. Obviously, you need to consider the compatibility of the code you want to support. For example, does the project run on good support for HTML5/CSS3

Combine JSLite and javascript native code when necessary

As mentioned above, JSLite is javascript, which means that anything you can do with JSLite can also be done with native code. Native code may not be as readable and maintainable as JSLite, and the code may be 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).

Final advice

Finally, I record this article with the purpose of improving the performance of JSLite and some other good suggestions. If you want to delve deeper into this topic you will find a lot of fun. Remember, JSLite is not required, just an option. Think about why you want to use it. DOM manipulation? ajax? stencil? css animation? Or a selector? Heavy jQuery developer?