JavaScript 数组高阶方法

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1) Current Task & Steps

Current task: Step 1 - 第一步：筛选完成任务并提取标题
实现 getCompletedTitles(tasks)，返回已完成任务标题，用逗号连接

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: getCompletedTitles(tasks)
Self-check: getCompletedTitles([{"title":"A","done":true},{"title":"B","done":false},{"title":"C","done":true}]) => "A,C"

2) Beginner Explanation (Current Step)

Step task: 实现 getCompletedTitles(tasks)，返回已完成任务标题，用逗号连接
Define function(s): getCompletedTitles, 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 getCompletedTitles(tasks) {
  return null;
}
// Self-check: getCompletedTitles([{"title":"A","done":true},{"title":"B","done":false},{"title":"C","done":true}]) should return "A,C"
console.log(getCompletedTitles([{"title":"A","done":true},{"title":"B","done":false},{"title":"C","done":true}]));

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 getCompletedTitles
返回完成任务标题

🔐 学习提示

📖 快速参考

some 返回 true/false，不会返回满足条件的那个值。

About This Exercise

数组高阶方法的目标是：用更短、更清晰的代码处理列表数据。

你可以先记四个分工：

filter：筛选“要哪些”
map：转换“变成什么”
reduce：汇总“算成一个值”
some：判断“有没有至少一个满足”

Beginner⏱ 25-30 min

Learning Objectives

理解四个高频数组方法的职责分工
掌握 filter + map 的链式写法
掌握 reduce 进行金额/分数汇总
掌握 some 进行风险条件检测

Scenario

你在做一个学习看板：需要展示已完成任务标题、统计总金额，并检测是否存在高风险分数。

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