JavaScript 默认参数

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1) Current Task & Steps

Current task: Step 1 - 问候函数
实现 greet(name = "Guest")，返回 "Hello, {name}"

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: greet(nameGuest)
Self-check: greet() => "Hello, Guest"
Self-check: greet("Amy") => "Hello, Amy"

2) Beginner Explanation (Current Step)

Step task: 实现 greet(name = "Guest")，返回 "Hello, {name}"
Define function(s): greet, 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 greet(nameGuest) {
  return null;
}
// Self-check: greet() should return "Hello, Guest"
console.log(greet());

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 greet
greet() 返回默认值
greet("Amy") 返回传入值

🔐 学习提示

📖 快速参考

默认参数能让调用方不必每次都传完整参数。

About This Exercise

默认参数就是“没传值时给一个备用值”。

这能避免新手常见错误：参数没传导致结果是 undefined。

Beginner⏱ 15-20 min

Learning Objectives

使用默认参数
处理可选输入
输出稳定结果

Scenario

你在实现工具函数时，希望调用方即使不传参数也能得到可预测结果。

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