offsetLeft 获取的是相对于父对象的左边距
left 获取或设置相对于 具有定位属性(position定义为relative)的父对象 的左边距
如果父div的position定义为relative,子div的position定义为absolute,那么子div的style.left的值是相对于父div的值,
这同offsetLeft是相同的,区别在于:
1. style.left 返回的是字符串,如28px,offsetLeft返回的是数值28,如果需要对取得的值进行计算,
还用offsetLeft比较方便。
2. style.left是读写的,offsetLeft是只读的,所以要改变div的位置,只能修改style.left。
3. style.left的值需要事先定义,否则取到的值为空。而且必须要定义在html里,我做过试验,如果定义在
css里,style.left的值仍然 为空,这就是我刚开始碰到的问题,总是取不到style.left的值。
offsetLeft则仍然能够取到,无需事先定义div的位置。

HTML, CSS and JavaScript are the core technologies for building modern web pages: 1. HTML defines the web page structure, 2. CSS is responsible for the appearance of the web page, 3. JavaScript provides web page dynamics and interactivity, and they work together to create a website with a good user experience.

The function of HTML is to define the structure and content of a web page, and its purpose is to provide a standardized way to display information. 1) HTML organizes various parts of the web page through tags and attributes, such as titles and paragraphs. 2) It supports the separation of content and performance and improves maintenance efficiency. 3) HTML is extensible, allowing custom tags to enhance SEO.

The future trends of HTML are semantics and web components, the future trends of CSS are CSS-in-JS and CSSHoudini, and the future trends of JavaScript are WebAssembly and Serverless. 1. HTML semantics improve accessibility and SEO effects, and Web components improve development efficiency, but attention should be paid to browser compatibility. 2. CSS-in-JS enhances style management flexibility but may increase file size. CSSHoudini allows direct operation of CSS rendering. 3.WebAssembly optimizes browser application performance but has a steep learning curve, and Serverless simplifies development but requires optimization of cold start problems.

The roles of HTML, CSS and JavaScript in web development are: 1. HTML defines the web page structure, 2. CSS controls the web page style, and 3. JavaScript adds dynamic behavior. Together, they build the framework, aesthetics and interactivity of modern websites.

The future of HTML is full of infinite possibilities. 1) New features and standards will include more semantic tags and the popularity of WebComponents. 2) The web design trend will continue to develop towards responsive and accessible design. 3) Performance optimization will improve the user experience through responsive image loading and lazy loading technologies.

The roles of HTML, CSS and JavaScript in web development are: HTML is responsible for content structure, CSS is responsible for style, and JavaScript is responsible for dynamic behavior. 1. HTML defines the web page structure and content through tags to ensure semantics. 2. CSS controls the web page style through selectors and attributes to make it beautiful and easy to read. 3. JavaScript controls web page behavior through scripts to achieve dynamic and interactive functions.

HTMLisnotaprogramminglanguage;itisamarkuplanguage.1)HTMLstructuresandformatswebcontentusingtags.2)ItworkswithCSSforstylingandJavaScriptforinteractivity,enhancingwebdevelopment.

HTML is the cornerstone of building web page structure. 1. HTML defines the content structure and semantics, and uses, etc. tags. 2. Provide semantic markers, such as, etc., to improve SEO effect. 3. To realize user interaction through tags, pay attention to form verification. 4. Use advanced elements such as, combined with JavaScript to achieve dynamic effects. 5. Common errors include unclosed labels and unquoted attribute values, and verification tools are required. 6. Optimization strategies include reducing HTTP requests, compressing HTML, using semantic tags, etc.


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