JavaScript 发布订阅模式

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Complete current Step 1 first

1) Current Task & Steps

Current task: Step 1 - 第一步：创建事件总线
实现 createBus()，包含 on 与 emit 方法

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: createBus(value)
Define function: testBusBasic(value)
Self-check: testBusBasic(undefined) => "ok"

2) Beginner Explanation (Current Step)

Step task: 实现 createBus()，包含 on 与 emit 方法
Define function(s): createBus, testBusBasic, 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 createBus(value) {
  return null;
}
function testBusBasic(value) {
  return null;
}

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 createBus
定义 testBusBasic
basic emit works

🔐 学习提示

📖 快速参考

emit 时事件名必须和 on 注册时完全一致，否则订阅函数不会执行。

About This Exercise

发布订阅（Pub/Sub）可以理解成“广播站”：

发布者（publish）只负责发消息
订阅者（subscribe）决定要不要听这条消息

发布者不需要知道谁在听，这就是“解耦”。

Intermediate⏱ 25-30 min

Learning Objectives

理解发布者与订阅者角色分离
掌握最小事件总线 API（on/emit）
支持多订阅者与 payload 透传

Scenario

你在做学习消息中心：一个模块发出“任务完成”事件，多个模块（通知、积分、日志）都要响应。

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