DOM 或文档对象模型是一个编程接口，它以元素树的形式表示网页的结构。它充当网页内容（HTML 和 CSS）与操作该内容的脚本或程序之间的桥梁。开发人员使用 DOM 来动态更新页面的内容、样式或行为，从而启用交互式表单、动画或响应式元素等功能。
DOM 是如何工作的？
当浏览器加载网页时，它会解析 HTML 和 CSS 并创建一个 DOM 树，其中每个节点代表一个元素、属性或一段文本。例如：
- <h1>标签成为页眉的节点。
- <p>标签为段落创建节点。
开发人员可以使用 JavaScript 或其他脚本语言来访问和操作这些节点。例如，他们可能会更改标题文本、更新样式或动态删除整个章节，所有这些都无需重新加载页面。
DOM 在 Web 抓取中的作用
网页抓取工具与 DOM 交互，从网页中提取特定数据。他们浏览 DOM 树来查找和检索产品价格、名称或评论等元素。代理通常通过使抓取器能够访问多个页面而不会被屏蔽来补充此过程。
DOM 是现代 Web 开发的基础概念，它使构建动态和交互式网站变得更加容易，同时也是自动数据提取工作流程的关键组件。
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用例
Dynamic Content Updates
When JavaScript changes a page, like showing a pop-up, hiding a menu, or loading new posts without a refresh, it’s manipulating the DOM. The script selects elements using methods like document.querySelector() and updates their content or attributes in real time.
Web Scraping and Automation
Tools such as Puppeteer, Selenium, or Playwright rely on the DOM to locate and extract elements. They don’t read HTML directly; they interact with the structured DOM, just like a browser does when rendering a live page.
Rendering Simulations
Headless browsers and testing frameworks simulate real browsers by constructing and manipulating the DOM. This helps developers and automation systems understand how JavaScript-driven sites load and behave before data is collected.
最佳实践
Access Elements Efficiently
Use document.querySelector() and document.querySelectorAll() instead of older methods like getElementById() or getElementsByClassName(). These methods are more flexible and align with CSS selectors.
Avoid Over-Manipulation
Frequent or unnecessary DOM changes can slow performance because each modification triggers a re-render. Group updates or use frameworks that manage virtual DOMs efficiently, like React.
Understand the CSSOM
The CSS Object Model (CSSOM) complements the DOM by representing CSS styles. Together, they form the render tree, which determines what users actually see.
Use Proxies Wisely in Automation
When scraping or automating, always ensure the DOM is fully loaded before extracting data. If a proxy rotates too early or the page hasn’t finished rendering, you may collect incomplete or empty data.
结论
The DOM transforms web pages from static code into interactive environments. It’s the browser’s way of interpreting and manipulating HTML and CSS, enabling developers and automated systems to dynamically modify content, extract information, and simulate real user actions.
From modern UIs to large-scale data scraping, the DOM is the invisible structure that makes the web come alive.
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经常问的问题
What does DOM stand for?
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DOM stands for Document Object Model—a structured representation of a web document as a tree of objects.
Is the DOM the same as HTML?
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No. HTML is the source code; the DOM is the in-memory structure the browser builds from that code.
Can I interact with the DOM without JavaScript?
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Not directly. CSS can style the DOM, but only JavaScript (or tools simulating it) can dynamically change or inspect it.
Why is the DOM important for web scraping?
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Because scrapers extract data from the rendered DOM, not raw HTML. Many modern websites load key data dynamically—visible only in the DOM after JavaScript executes.
