


JavaScript study notes one: jQuery writing method, image scaling and preloading_jquery
One of the JavaScript study notes: jQuery writing method, image scaling and preloading
In the past, when using JavaScript, I always wrote a few functions on the page, and basically did not consider the encapsulation and reuse of functions. Recently, there has been This project may have high requirements in this regard, so I researched encapsulation similar to jQuery.
Here, let’s try the effects of image scaling and preloading, and write similar JavaScript code.
The effect of image scaling and preloading is as follows (the preloading effect is sometimes not very obvious):
The main JS code is as follows:
(function() {
var yQuery = (function() {
var yQuery = function () {
return yQuery.fn.init();
};
yQuery.fn = yQuery.prototype = {
init: function() {
return this;
},
//Image proportional scaling and preloading method declaration, but I feel that writing it like this (return new imgResizeBox(e)) is very awkward. Please let me know.
imgResize: function(e) {
return new imgResizeBox( e);
}
};
//image image processing
var imgResizeBox = function(e) {
//image parameter
setting = {
imgId: " ", //The ID of the image container, such as .viewArea img
height: 0,
width: 0,
loading: "images/lightbox-ico-loading.gif"
};
$.extend(setting, e, setting); //Parameter replacement
var images = $(setting.imgId); //Get all images
$(images).hide(); //Hide
var loading = new Image(); //Preload images
loading.className = "loading";
loading.src = setting.loading;
$(images).after(loading);
//Preloading function
var perLoading = function($this) {
var img = new Image();
img.src = $this.src;
if (img. complete) {
computeImg.call($this);
return;
};
img.onload = function() {
computeImg.call($this);
img .onload = function() { };
};
};
//Picture scaling processing, and picture display function
var computeImg = function() {
var m = this.height - setting.height;
var n = this.width - setting.width;
if (m > n)
this.height = this.height > setting.height ? setting .height : this.height;
else
this.width = this.width > setting.width ? setting.width : this.width;
$(this).next(".loading") .remove();
$(this).show();
};
//Call the preloading function in a loop
return $(images).each(function() {
perLoading(this);
});
}
return yQuery;
})();
window.yQuery = window.$$ = yQuery();
}) ();
The calling code is as follows:
$(document).ready(function()
{
$$.imgResize({ imgId: ".viewArea img", height:160, width:270, loading: "http:// www.jb51.net/images/2012/155618/2012062710243954.gif" });
});
Finally, the simple source code is attached: jsDemo_jb51.rar

Yes, the engine core of JavaScript is written in C. 1) The C language provides efficient performance and underlying control, which is suitable for the development of JavaScript engine. 2) Taking the V8 engine as an example, its core is written in C, combining the efficiency and object-oriented characteristics of C. 3) The working principle of the JavaScript engine includes parsing, compiling and execution, and the C language plays a key role in these processes.

JavaScript is at the heart of modern websites because it enhances the interactivity and dynamicity of web pages. 1) It allows to change content without refreshing the page, 2) manipulate web pages through DOMAPI, 3) support complex interactive effects such as animation and drag-and-drop, 4) optimize performance and best practices to improve user experience.

C and JavaScript achieve interoperability through WebAssembly. 1) C code is compiled into WebAssembly module and introduced into JavaScript environment to enhance computing power. 2) In game development, C handles physics engines and graphics rendering, and JavaScript is responsible for game logic and user interface.

JavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.

Python is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.

C and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.


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