HTML:
JS:
window.onload=function(e){ var text=document.getElementById("only"),pattern=/\d/,//pattern匹配字母上的数字键 pattern2=/(9[6-9])|(10[0-5])|3(7|9)/,//pattern2匹配小键盘上的数字键和左右方向键 EventHandle={},event=e||window.event;//一个处理事件的对象 //当网页加载的时候,进行判断,对事件处理对象进行定义属性,这样对事件对象的方法只需要进行一次判断,以后的其他事件 //处理程序里面不需要判断 if(event.preventDefault){ EventHandle.preventDefault=function(e){ e.preventDefault(); }; }else{ EventHandle.preventDefault=function(e){ e.returnValue=false; } } text.onkeydown=function(e){ var event=e||window.event;//不同事件的事件对象不一样,这个event和最前面的event不相等 if(!pattern.test(String.fromCharCode(event.keyCode))&&event.keyCode!=8//keyCode=8是退格键,因为可以对输入的数字进行修改,所以退格和左右方向键不禁止 &&!pattern2.test(event.keyCode.toString())||event.shiftKey|| event.ctrlKey||event.metaKey){ EventHandle.preventDefault(event);//如果不用对象的这个方法,写成下面这样,也可以执行,不过每次按下键盘的时候都会进行一次判断 //这个是没有必要的,所以在页面加载的时候对事件处理对象定义一个方法,加载后对象的方法就已经是确定的了,以后时候就可以了 //if(event.preventDefault){ //event.preventDefault(); //}else{ //event.returnValue=false; //} } } }
Uncommented version:
window.onload=function(e){ var text=document.getElementById("only"),pattern=/\d/, pattern2=/(9[6-9])|(10[0-5])|3(7|9)/, EventHandle={},event=e||window.event; if(event.preventDefault){ EventHandle.preventDefault=function(e){ e.preventDefault(); }; }else{ EventHandle.preventDefault=function(e){ e.returnValue=false; } } text.onkeydown=function(e){ var event=e||window.event; if(!pattern.test(String.fromCharCode(event.keyCode))&&event.keyCode!=8 &&!pattern2.test(event.keyCode.toString())||event.shiftKey|| event.ctrlKey||event.metaKey){ EventHandle.preventDefault(event); } } }
In IE11, F12 opens the developer tools and you can select the IE version for debugging

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.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.


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