JavaScript 展开与剩余参数

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1) Current Task & Steps

Current task: Step 1 - 合并标签列表
实现 mergeTags(a, b)，返回合并后的字符串，格式 "x|y|z"

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: mergeTags(a, b)
Self-check: mergeTags(["js","ts"], ["react"]) => "js|ts|react"

2) Beginner Explanation (Current Step)

Step task: 实现 mergeTags(a, b)，返回合并后的字符串，格式 "x|y|z"
Define function(s): mergeTags, 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 mergeTags(a, b) {
  return '';
}
// Self-check: mergeTags(["js","ts"], ["react"]) should return "js|ts|react"
console.log(mergeTags(["js","ts"], ["react"]));

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 mergeTags
mergeTags 返回正确

🔐 学习提示

📖 快速参考

spread/rest 在 React props、函数参数、状态更新中非常高频。

About This Exercise

很多新手会问：为什么同样是 ...，有时是展开，有时是收集？

这关用三个任务讲清楚：数组里是“展开”，函数参数里是“收集”。

Intermediate⏱ 20-25 min

Learning Objectives

使用 spread 合并数组
使用 rest 接收不定参数
理解两者区别

Scenario

你在写工具函数：先合并标签数组，再做可变参数求和，最后把结果去重排序。这是项目中非常常见的真实组合。

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