JavaScript 字符串方法

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1) Current Task & Steps

Current task: Step 1 - 先格式化：统一名字大小写
定义 capitalize 函数，将字符串的首字母大写，其余小写。

Write your code in `script.js` for the current Step.
Click "Run Validation" to check if rules pass.
Once current Step passes, the next step unlocks automatically.
You need to pass Step 1 first to unlock Step 2.

Step Deliverables (Check these)

Define function: capitalize(value)
Self-check: capitalize("hELLO") => "Hello"

2) Beginner Explanation (Current Step)

Step task: 定义 capitalize 函数，将字符串的首字母大写，其余小写。
Define function(s): capitalize, then verify results with test inputs.
This step has a specific expected result. Focus on making the function return the correct value.
A function is a reusable block of code. Define it first, then call it.
`return` sends a result back. Without return, you usually can't get the function's result.

3) Starter Template (Type along)

function capitalize(value) {
  return '';
}
// Self-check: capitalize("hELLO") should return "Hello"
console.log(capitalize("hELLO"));

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 capitalize 函数
capitalize("hELLO") 返回 "Hello"

💡 步骤提示

🔐 学习提示

📖 快速参考

模板字符串要用反引号 ...，不是单引号或双引号。

About This Exercise

前端每天都在处理字符串：用户名、标题、搜索词、邮箱输入。

这关只练最常用的三类能力：

你将学到：

格式化：首字母大写，其余小写
拼接：模板字符串输出完整文案
校验：判断是否包含特定符号

Beginner⏱ 15-20 min

Learning Objectives

掌握 toUpperCase/toLowerCase/slice 的组合用法
掌握模板字符串插值语法
掌握 includes 的基础校验写法
理解字符串方法返回新值而非修改原值

Scenario

你在做注册表单：要格式化用户名显示、拼接欢迎语、检查输入是否像邮箱。

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

All rules for the current step passCan explain each line of your codeCan name a real-world business scenario for this

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?

Not confident yet, need more practiceCan complete similar tasks independentlyCan teach others how to do it