Decorators — Animate | AI Wisdom

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🎞 ANIMATE · Mode 3 of 5 · +100 XP— TypeScript Decorators
📋Class Dec.
⚙️Method Dec.
🔄Field Dec.
✅Factories
🎯 Next: Test →
Step 1 / 4
Speed
Class Decorator
@sealed — class decorator seals the constructor and prototype💡 Analogy
Like laminating a document — you can read it but can't add new sticky notes to it.
A class decorator is a function that receives the class constructor. @sealed calls Object.seal() to prevent adding new properties to the class or prototype.
Console Output
> @sealed applied to BugReport
> Object.seal(BugReport) — no new static props
> Object.seal(BugReport.prototype) — no new instance props
●decorators.ts
Class DecoratorL4–13
1// TypeScript 5 decorators (Stage 3 proposal)
2 
3// Class decorator — adds metadata
4function sealed(ctor: new (...args: any[]) => any) {
5  Object.seal(ctor);
6  Object.seal(ctor.prototype);
7}
8 
9@sealed
10class BugReport {
11  type = 'report';
12  title: string;
13  constructor(t: string) { this.title = t; }
14}
15 
16// Method decorator — log execution time
17function logTime(originalMethod: Function, context: ClassMethodDecoratorContext) {
18  return function (this: any, ...args: any[]) {
19    const start = performance.now();
20    const result = originalMethod.call(this, ...args);
21    console.log(`${String(context.name)}: ${performance.now() - start}ms`);
22    return result;
23  };
24}
25 
26class DataService {
27  @logTime
28  async fetchAll() {
29    return fetch('/api/data').then(r => r.json());
30  }
31}
32 
33// Property decorator — validation
34function minLength(min: number) {
35  return function (target: undefined, context: ClassFieldDecoratorContext) {
36    return function (this: any, value: string) {
37      if (value.length < min) throw new Error(`Min ${min} chars required`);
38      return value;
39    };
40  };
41}
41 lines
Timeline — 4 Steps
Class Decorator
@sealed — class decorator seals the constructor and prototype💡 Analogy
Like laminating a document — you can read it but can't add new sticky notes to it.
A class decorator is a function that receives the class constructor. @sealed calls Object.seal() to prevent adding new properties to the class or prototype.
Console Output
> @sealed applied to BugReport
> Object.seal(BugReport) — no new static props
> Object.seal(BugReport.prototype) — no new instance props

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Discussion

@sealed — class decorator seals the constructor and prototype

💡 Analogy

Like laminating a document — you can read it but can't add new sticky notes to it.

A class decorator is a function that receives the class constructor. @sealed calls Object.seal() to prevent adding new properties to the class or prototype.

Console Output

> @sealed applied to BugReport
> Object.seal(BugReport) — no new static props
> Object.seal(BugReport.prototype) — no new instance props

@sealed — class decorator seals the constructor and prototype

💡 Analogy

Like laminating a document — you can read it but can't add new sticky notes to it.

A class decorator is a function that receives the class constructor. @sealed calls Object.seal() to prevent adding new properties to the class or prototype.

Console Output

> @sealed applied to BugReport
> Object.seal(BugReport) — no new static props
> Object.seal(BugReport.prototype) — no new instance props