JavaScript 状态机模式

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1) Current Task & Steps

Current task: Step 1 - 第一步：写状态转移函数
实现 nextState(state, event) 支持 draft->review->done

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: nextState(state, event)
Self-check: nextState("draft", "submit") => "review"
Self-check: nextState("review", "approve") => "done"

2) Beginner Explanation (Current Step)

Step task: 实现 nextState(state, event) 支持 draft->review->done
Define function(s): nextState, 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 nextState(state, event) {
  return null;
}
// Self-check: nextState("draft", "submit") should return "review"
console.log(nextState("draft", "submit"));

4) Rule Validation & Hints

📋 当前任务 - Step 1

定义 nextState
draft submit -> review
review approve -> done

🔐 学习提示

📖 快速参考

不要把所有逻辑塞进 if-else 大泥球，先明确“状态”和“事件”再写代码。

About This Exercise

状态机适合“有阶段”的业务流程，例如审批、订单、任务状态。

核心公式只有一条：

当前状态 + 事件 = 下一状态

好处是流程可控，非法跳转能被拦住。

Intermediate⏱ 25-30 min

Learning Objectives

掌握状态转移函数的设计方式
处理非法流转的兜底逻辑
能根据事件序列推演最终状态

Scenario

你在做审批流：草稿可以提交到审核，审核通过进入完成，审核拒绝回到草稿。任何不合法事件都要保持原状态。

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