DrillLab
开始StartNode.js, npm, node_modules and the lockfile
练习Practice

动手做Get your hands on it

练习跟着课文走 —— 每节课尾都有本课的练习。这一页是全部练习的总库，想集中刷题的时候来。 每个练习都写清了它来自哪一节，卡住了就回去看那一节。Practice follows the lessons — every lesson ends with the exercises for that lesson. This page is the whole library, for when you want to drill in one sitting. Each exercise names the lesson it came from, so you can go back when you stall.

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筛一下Filter theseL2L2
课程Course全部All地基 · 项目与语言Foundations · project and languageReact 考试React examFederation 考试Federation exam面试八股Interview questionsCab BookingCab Booking
难度LevelL1 → L4 和上面四档同一个意思：给你的东西越来越少L1 → L4: the same idea as the four tiers above — less is handed to you全部难度All levelsL1L1L2L2L3L3L4L4
类型Kind全部类型All kinds认出来Spot it排顺序Order it填空Fill the blanks写整块Write a blockDebug LabDebug Lab从零重写Rebuild from scratch

练习Exercises

筛出 47 个练习（共 148 个） · 第 1 / 4 页。Showing 47 of 148 · page 1 / 4.
来自From package.json 逐字段读一遍package.json, field by field · 地基 · 项目与语言Foundations · project and language
L2填空Fill the blanks补全 subgraph 的 package.json 关键字段Fill in the key fields of the subgraph package.json

下面是 node-subgraph/package.json 的骨架，挖掉了三个决定项目行为的值。 照真实文件补回来。

Below is the skeleton of node-subgraph/package.json with three values removed. Each one decides how the project behaves. Put them back the way the real file has them.

JSONnode-subgraph/package.json3 个空3 blanks
1{
2 "name": "order-subgraph",
3 "main": "src/index.js",
4 "type": "",
5 "scripts": {
6 "start": "node src/index.js",
7 "test": "NODE_OPTIONS=--experimental-vm-modules "
8 },
9 "dependencies": {
10 "@apollo/server": "^4.10.0",
11 "@apollo/subgraph": "^2.7.0",
12 "graphql": "^16.8.1",
13 "graphql-tag": "^2.12.6",
14 "": "^2.2.2"
15 }
16}
把 3 个空都填上才能检查（还差 3 个）Fill all 3 blanks to check (3 to go)
来自From 数组与对象：不可变更新三件套Arrays and objects: three ways to update without changing the original · 地基 · 项目与语言Foundations · project and language
L2填空Fill the blanks补全 Q1 的三个数据操作Fill in the three data operations of Q1

这是 NoteManager 里三个 handler 的真实代码， 挖掉了决定行为的关键词。想清楚每个操作要「保留多少条」再填。

This is the real code of the three handlers in NoteManager, with the words that decide the behaviour removed. Before you fill each one in, work out how many items that operation has to keep.

TSXsrc/components/NoteManager/index.tsx4 个空4 blanks
1const handleSubmitNote = (submittedNote: Note) => {
2 if (noteToEdit) {
3 setNotes((prev) =>
4 prev.((note) =>
5 note.id === submittedNote.id ? submittedNote : note,
6 ),
7 );
8 setNoteToEdit(null);
9 } else {
10 setNotes((prev) => [, submittedNote]);
11 }
12};
13
14const handleDelete = (id: number) => {
15 setNotes((prev) => prev.((note) => note.id id));
16};
把 4 个空都填上才能检查（还差 4 个）Fill all 4 blanks to check (4 to go)
来自From 数组与对象：不可变更新三件套Arrays and objects: three ways to update without changing the original · 地基 · 项目与语言Foundations · project and language
L2Debug LabDebug LabDebug Lab · 数据加进去了，界面没反应Debug Lab · the data went in, the screen did not move

这一类 bug 最难查，因为它不报错。 先看现象，判断类型，再找病灶 —— 别跳步。

This kind of bug is the hardest to find, because it reports no error. Read the symptom, classify it, then locate it. Do not skip a step.

第 1 步 · 先看现象和代码，别急着改Step 1 · read the symptom and the code before you touch anything
# 没有任何报错。控制台干净。 # 现象：填好表单点 Add，表格里什么都不出现。 # 在 handleSubmitNote 里 console.log(notes) —— 长度确实在增加。 notes.length before: 0 notes.length after : 1 ← 数据真的进去了 （但 <NoteTable /> 渲染出来的行数始终是 0）# No error at all. The console is clean. # Symptom: fill in the form, click Add, and nothing shows up in the table. # Add console.log(notes) inside handleSubmitNote — the length really does grow. notes.length before: 0 notes.length after : 1 ← the data really did go in (But <NoteTable /> always renders 0 rows.)
TSX有问题的写法The broken version示意Illustrative
1const handleSubmitNote = (submittedNote: Note) => {
2 notes.push(submittedNote);
3 setNotes(notes);
4};
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 异步：Promise、await、all 和 allSettledAsync: Promise, await, all and allSettled · 地基 · 项目与语言Foundations · project and language
L2填空Fill the blanks补全 DataLoader 的批量函数Fill in the batch function of the DataLoader

这是 subgraph 里真实的 DataLoader 批量加载函数。 两个空都关系到「异步 + 数组」的固定套路。

This is the real DataLoader batch function from the subgraph. Both blanks are part of the fixed pattern for async work over an array.

JSsrc/resolvers/orderResolvers.js2 个空2 blanks
1function createShippingInfoLoader(shippingDataSource) {
2 return new DataLoader(async orderIds => {
3 const shippingInfos = await Promise.(
4 orderIds.(id => shippingDataSource.getShippingInfo(id))
5 );
6
7 return shippingInfos;
8 });
9}
把 2 个空都填上才能检查（还差 2 个）Fill all 2 blanks to check (2 to go)
来自From ESM:import / export 与那些莫名其妙的报错ESM: import / export, and the errors that look strange at first · 地基 · 项目与语言Foundations · project and language
L2Debug LabDebug LabDebug Lab · ERR_MODULE_NOT_FOUNDDebug Lab · ERR_MODULE_NOT_FOUND

你在 node-subgraph/ 里跑 npm start, 服务器起不来。报错很长，但关键信息只有两行。

You run npm start inside node-subgraph/ and the server does not come up. The error is long, but only two lines of it matter.

第 1 步 · 先看现象和代码，别急着改Step 1 · read the symptom and the code before you touch anything
$ npm start node:internal/modules/esm/resolve:274 Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/Users/me/node-subgraph/src/dataSources/orderDataSource' imported from /Users/me/node-subgraph/src/index.js at finalizeResolution (node:internal/modules/esm/resolve:274:11) Did you mean to import "./dataSources/orderDataSource.js"?
JavaScriptsrc/index.js（第 2 行有问题）src/index.js (line 2 is the problem)示意Illustrative
1import { resolvers } from './resolvers/orderResolvers.js';
2import { OrderDataSource } from './dataSources/orderDataSource';
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 类型、type 与 interfaceTypes, type and interface · 地基 · 项目与语言Foundations · project and language
L2填空Fill the blanks补全 NoteTable 的 props 类型Fill in the props type of NoteTable

这是 NoteTable 真实的 props 类型。 三个空：一个数组类型、一个函数类型的参数、一个函数类型的返回值。

This is the real props type of NoteTable. Three blanks: an array type, a parameter of a function type, and the return value of a function type.

TSXsrc/components/NoteTable/index.tsx3 个空3 blanks
1export interface NoteTableProps {
2 notes: ;
3 onDelete: (id: ) => void;
4 onEdit: (note: Note) => ;
5}
把 3 个空都填上才能检查（还差 3 个）Fill all 3 blanks to check (3 to go)
来自From 泛型参数，以及怎么读 tsc 的报错Generic parameters, and how to read a tsc error · 地基 · 项目与语言Foundations · project and language
L2填空Fill the blanks补全泛型参数Fill in the generic parameters

两处真实的泛型用法。想清楚「TypeScript 能不能自己推断出来」。

Two real uses of generics. For each one, work out whether TypeScript can infer it on its own.

TSX两个真实片段Two real snippets3 个空3 blanks
1// NoteManager：两个 state
2const [notes, setNotes] = useState<>([]);
3const [noteToEdit, setNoteToEdit] = useState<Note | >(null);
4
5// q2/taskRunner.ts：自定义泛型
6export type Task<T> = () => <T>;
把 3 个空都填上才能检查（还差 3 个）Fill all 3 blanks to check (3 to go)
来自From props：数据往下流，事件往上报props: data flows down, events go back up · React 考试React exam
L2填空Fill the blanks补全 NoteItem 的两个按钮Fill in the two buttons of NoteItem

这是 NoteItem 真实的两个按钮。 一个要传整条笔记，一个只传 id —— 想清楚各自要传什么， 以及怎么才能「点击时才执行」。

These are the two real buttons of NoteItem. One passes the whole note, the other passes only the id. Decide what each one has to pass, and how to make it run only on the click.

TSXsrc/components/NoteItem/index.tsx2 个空2 blanks
1<td>
2 <button onClick={ onEdit(note)} className="outlined">
3 Edit
4 </button>
5</td>
6<td>
7 <button onClick={() => onDelete()} className="danger">
8 Delete
9 </button>
10</td>
把 2 个空都填上才能检查（还差 2 个）Fill all 2 blanks to check (2 to go)
来自From props：数据往下流，事件往上报props: data flows down, events go back up · React 考试React exam
L2Debug LabDebug LabDebug Lab · 页面一打开，所有笔记就消失了Debug Lab · every note disappears the moment the page opens

添加两条笔记后刷新页面（假设有持久化），表格瞬间变空。 有时候浏览器还会卡住。先判断类型，再找病灶。

Add two notes, then reload the page (assume the notes are saved somewhere). The table goes empty at once, and sometimes the browser stops responding. First name the kind of error, then find the line that causes it.

第 1 步 · 先看现象和代码，别急着改Step 1 · read the symptom and the code before you touch anything
Warning: Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of nested updates to prevent infinite loops. （另一种表现：没有任何报错，但表格永远是空的）Warning: Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of nested updates to prevent infinite loops. (Another symptom: no warning at all, but the table stays empty forever.)
TSX有问题的 NoteItemThe NoteItem with the bug示意Illustrative
1const NoteItem: React.FC<NoteItemProps> = ({ note, onDelete, onEdit }) => {
2 return (
3 <tr>
4 <td>{note.title}</td>
5 <td>{note.content}</td>
6 <td>
7 <button onClick={onEdit(note)} className="outlined">Edit</button>
8 </td>
9 <td>
10 <button onClick={onDelete(note.id)} className="danger">Delete</button>
11 </td>
12 </tr>
13 );
14};
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From 受控输入：value + onChange 的闭环Controlled inputs: the loop between value and onChange · React 考试React exam
L2填空Fill the blanks补全受控输入的闭环Complete the loop of a controlled input

把 NoteForm 里 textarea 那一段补全。 三个空构成一个完整的闭环。

Fill in the textarea part of NoteForm. The three blanks together form one complete loop.

TSXsrc/components/NoteForm/index.tsx3 个空3 blanks
1const [content, setContent] = ("");
2
3<textarea
4 placeholder="Content"
5 value={}
6 onChange={(e) => setContent()}
7 data-testid="form-textarea"
8 className="form-textarea"
9/>
把 3 个空都填上才能检查（还差 3 个）Fill all 3 blanks to check (3 to go)
来自From 受控输入：value + onChange 的闭环Controlled inputs: the loop between value and onChange · React 考试React exam
L2Debug LabDebug LabDebug Lab · 点 Add 之后页面闪一下，笔记没了Debug Lab · the page blinks after Add and the note is gone

填好标题和内容，点 Add。页面明显闪了一下， 地址栏出现了 ?，表格还是空的。

Fill in a title and some content, then press Add. The page clearly blinks, a ? appears in the address bar, and the table is still empty.

第 1 步 · 先看现象和代码，别急着改Step 1 · read the symptom and the code before you touch anything
# 没有 JavaScript 报错。 # 现象：点击 Add 后 # - 页面整体刷新了一次 # - 地址栏从 http://localhost:5173/ 变成 http://localhost:5173/? # - 输入框被清空，表格依然是空的 # - React DevTools 里所有 state 都回到了初始值# No JavaScript error. # Symptom: after clicking Add # - the whole page reloaded once # - the address bar changed from http://localhost:5173/ to http://localhost:5173/? # - the inputs were cleared and the table is still empty # - in React DevTools every piece of state is back to its initial value
TSX有问题的 handleSubmitThe broken handleSubmit示意Illustrative
1const handleSubmit = (event: React.FormEvent<HTMLFormElement>) => {
2 if (isFormInvalid) return;
3 const newNote = { id: Date.now(), title: title.trim(), content: content.trim() };
4 onSubmit(newNote);
5 setTitle("");
6 setContent("");
7};
第 2 步 · 这是什么类型的错误Step 2 · what kind of error is this
来自From useEffect：把 props 的变化同步进 stateuseEffect: copying a change in props into state · React 考试React exam
L2填空Fill the blanks补全编辑回填的 useEffectComplete the useEffect that prefills the form for editing

这是 NoteForm 里那个决定 Task 3 成败的 effect。 两个空：一个分支条件，一个依赖数组。

This is the effect in NoteForm that decides whether Task 3 passes. Two blanks: one branch condition, one dependency array.

TSXsrc/components/NoteForm/index.tsx2 个空2 blanks
1useEffect(() => {
2 if () {
3 setTitle(noteToEdit.title);
4 setContent(noteToEdit.content);
5 } else {
6 setTitle("");
7 setContent("");
8 }
9}, );
把 2 个空都填上才能检查（还差 2 个）Fill all 2 blanks to check (2 to go)