JavaScript 条件语句

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1) Current Task & Steps

Current task: Step 1 - 简单的 if 判断
定义一个 checkPass 函数，接收分数参数。如果分数 >= 60，返回 "Pass"，否则返回 "Fail"。

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: checkPass(value)
Self-check: checkPass(75) => "Pass"
Self-check: checkPass(45) => "Fail"

2) Beginner Explanation (Current Step)

Step task: 定义一个 checkPass 函数，接收分数参数。如果分数 >= 60，返回 "Pass"，否则返回 "Fail"。
Define function(s): checkPass, 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 checkPass(value) {
  return null;
}
// Self-check: checkPass(75) should return "Pass"
console.log(checkPass(75));

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 checkPass 函数
checkPass(75) 返回 "Pass"
checkPass(45) 返回 "Fail"

💡 步骤提示

🔐 学习提示

📖 快速参考

&& 和 || 有短路特性。a && b 如果 a 为假则直接返回 a；a || b 如果 a 为真则直接返回 a。

About This Exercise

条件语句的本质是：满足条件就走 A，不满足就走 B。

你会先写最直观的 if/else，再过渡到更简洁的三元表达式。

你将学到：

使用 if、else if、else 进行条件判断
比较运算符：===、!==、>、<
逻辑运算符：&&、||、!
三元运算符：条件 ? 值1 : 值2

Beginner⏱ 15-20 min

Learning Objectives

理解条件判断的概念
掌握 if/else 语法
学会使用比较和逻辑运算符
理解三元运算符的用法

Scenario

你在做成绩评级系统：输入分数，输出结果。这是最典型的新手条件判断场景。

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