JavaScript DOM 操作基础
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About This Exercise
DOM 可以理解成“网页的结构树”。
你看到的标题、按钮、卡片，本质上都是 DOM 元素。
学会 DOM 后，你就能用 JavaScript 改文字、改样式、改状态。
你将学到：
- 用
querySelector选中目标元素 - 修改
textContent更新页面文字 - 用
classList.add切换视觉状态 - 通过
style修改内联样式
Beginner⏱ 25-30 min
Learning Objectives
- 理解 DOM 是 JavaScript 操作网页的入口
- 掌握 querySelector 的基础选择方式
- 能完成文字、类名、样式三种常见更新
- 建立“先选元素，再改属性”的操作习惯
Scenario
你要做一个“状态提示卡片”：
页面加载后，标题变成欢迎文案，方块切到激活状态，并高亮背景色。
这就是最基础的前端动态交互流程。
Why Do This
- Frontend JS is not just about knowing the syntax — the key is reliably manipulating the DOM and managing interaction state.
- Break down the event flow (trigger -> handle -> update UI) before coding, and you will make significantly fewer errors.
- Rule-based validation helps you develop a testable frontend mindset.
Hands-on Practice
- Write out the event flow in comments first, then implement the functions.
- Add an edge case branch for invalid input or empty data.
- Explain why each validation rule is needed.
Common Mistakes
- Only testing the happy path without verifying edge inputs or repeated clicks.
- Mixing event binding and state updates together, making future maintenance difficult.
- Console output looks correct but the UI is not actually updated.
Deliverable
A reusable interaction component scaffold (event flow description + key functions + edge case handling).
My Progress
Completed Steps0 / 3
Total Attempts0
Best Score0%
Completion Criteria (Checkable)
Confirm before completing this Lab
Reflection Questions (Recommended)
Describe the event flow of this Lab in 2-3 sentences (trigger -> handle -> update).
What edge case did you add? Why is it easy to miss?
How confident are you with this interaction pattern now?
Tags
JavaScriptDOMquerySelectorWeb API