Variables, Data Types, and Interfaces in Angular (TypeScript)

These are foundational concepts that make your Angular app type-safe, scalable, and easier to maintain.

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🔹 1. Variables in TypeScript

TypeScript is strongly typed, so you can (and should) define the type of your variables.

✅ Syntax:

let name: string = "Angular";
const version: number = 17;
var isAwesome: boolean = true;

🔄 `let` vs `const` vs `var`:

Keyword	Scope	Reassignable	Hoisted
`let`	Block	✅ Yes	❌ No
`const`	Block	❌ No	❌ No
`var`	Function	✅ Yes	✅ Yes

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🔹 2. Data Types in TypeScript

Type	Example
`string`	`"Angular"`
`number`	`42`
`boolean`	`true`, `false`
`any`	Anything (use with caution)
`array`	`string[]`, `number[]`
`tuple`	`[string, number]`
`enum`	`enum Status { Active, Inactive }`
`object`	`{ name: string, age: number }`
`null` & `undefined`	`null`, `undefined`
`union`	`string | number`

Example:

let names: string[] = ["John", "Jane"];
let user: [string, number] = ["Alice", 30];

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🔹 3. Interfaces

Interfaces define the shape of objects. They're especially useful in Angular for defining models, HTTP responses, etc.

✅ Defining an Interface

interface User {
  id: number;
  name: string;
  email?: string; // Optional property
}

🛠 Using Interfaces

const user: User = {
  id: 1,
  name: "Alice"
};

👍 Interface with Functions

interface Greeter {
  greet(name: string): string;
}

class MyGreeter implements Greeter {
  greet(name: string): string {
    return `Hello, ${name}`;
  }
}

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🧠 Summary

• Use `let`, `const`, and define types for type safety.
• Leverage TypeScript’s strong typing to catch errors early.
• Use interfaces to describe complex object shapes clearly and enforce consistency.

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