Perfect jquery processing mechanism_jquery-JS Tutorial-php.cn

Home

Web Front-end

JS Tutorial

Perfect jquery processing mechanism_jquery

WBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWB

May 16, 2016 pm 03:14 PM

jquery

Using jQuery selectors is not only much simpler than using the traditional getElementById() and getElementsByTagName() functions, but it can also avoid certain errors. Please see the example below:

 <script>
  document.getElementById("div").style.color ="red";
 </script>

After running the above code, the browser will report an error because there is no element with the ID of div in the web page.

The improved code is as follows:

<script>
   if(document.getElementById("div")){ //用了IF语句来判断是否有ID为div的元素，如果有，执行下面代码 
    document.getElementById("div").style.color ="red"
   }
</script>

This can avoid browser errors, but if there are many elements to be operated, each element may have to be judged once, and jquery handles the problem very well, even if JQUERY is used to obtain the web page that does not exist Elements will not report an error.

The code is as follows:

 <script>
  $("#div").css("color","red");
 </script>

With this preventive measure, even if a previously used element on the webpage is deleted for some reason in the future, there is no need to worry that the JavaScript of this webpage will report an error.

Note:

$("div") always obtains a jquery object, even if there is no such element on the web page. So when you want to use jquery to check whether an element exists on the web page.

The following code cannot be used:

<script>
 if($("#div")){
   $("#div").css("color",red) //这样游览器会报错
  }
</script>

It should be judged based on the obtained length.

The code is as follows:

<script>
 if($("#div").length >0){
   $("#div").css("color",red)
 }
</script>

At this time, it can also be converted into a DOM object for judgment.

The code is as follows:

<body>
  <div id="div">ccccccc</div>
<script src="jquery-2.1.4.min.js"></script>
<script>
  var $div = $("#div");
  var div = $div[0];
  if(div){
    $div.css("color","red")  //此时DIV的颜色就变为red
  }
</script>
</body>

This is the perfect processing mechanism of jquery. I hope it will be helpful for everyone to learn jquery programming.

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Behind the Scenes: What Language Powers JavaScript?Apr 28, 2025 am 12:01 AM

JavaScript runs in browsers and Node.js environments and relies on the JavaScript engine to parse and execute code. 1) Generate abstract syntax tree (AST) in the parsing stage; 2) convert AST into bytecode or machine code in the compilation stage; 3) execute the compiled code in the execution stage.

The Future of Python and JavaScript: Trends and PredictionsApr 27, 2025 am 12:21 AM

The future trends of Python and JavaScript include: 1. Python will consolidate its position in the fields of scientific computing and AI, 2. JavaScript will promote the development of web technology, 3. Cross-platform development will become a hot topic, and 4. Performance optimization will be the focus. Both will continue to expand application scenarios in their respective fields and make more breakthroughs in performance.

Python vs. JavaScript: Development Environments and ToolsApr 26, 2025 am 12:09 AM

Both Python and JavaScript's choices in development environments are important. 1) Python's development environment includes PyCharm, JupyterNotebook and Anaconda, which are suitable for data science and rapid prototyping. 2) The development environment of JavaScript includes Node.js, VSCode and Webpack, which are suitable for front-end and back-end development. Choosing the right tools according to project needs can improve development efficiency and project success rate.

Is JavaScript Written in C? Examining the EvidenceApr 25, 2025 am 12:15 AM

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's Role: Making the Web Interactive and DynamicApr 24, 2025 am 12:12 AM

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: The Connection ExplainedApr 23, 2025 am 12:07 AM

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.

From Websites to Apps: The Diverse Applications of JavaScriptApr 22, 2025 am 12:02 AM

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 vs. JavaScript: Use Cases and Applications ComparedApr 21, 2025 am 12:01 AM

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.

See all articles