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Lesson Content

TypeScript Basic Types

TypeScript provides several basic types that you can use to annotate your variables, function parameters, and return values.

Primitive Types

// String
let name: string = "John";

// Number
let age: number = 30;

// Boolean
let isActive: boolean = true;

// Null and Undefined
let value: null = null;
let data: undefined = undefined;

Arrays

// Array of numbers
let numbers: number[] = [1, 2, 3];

// Alternative syntax
let names: Array = ["Alice", "Bob"];

Any Type

// Use sparingly - disables type checking
let anything: any = "can be anything";
anything = 42;
anything = true;

Void Type

// For functions that don't return anything
function logMessage(message: string): void {
  console.log(message);
}

Type Inference

// TypeScript can infer types
let count = 10; // inferred as number
let greeting = "Hello"; // inferred as string

Example Code

Practice using different TypeScript types

// Declare variables with proper types
let userName: string = "TypeScript";
let userAge: number = 5;
let isLearning: boolean = true;
let skills: string[] = ["JavaScript", "TypeScript"];

console.log(`Name: ${userName}, Age: ${userAge}`);
console.log(`Learning: ${isLearning}`);
console.log(`Skills: ${skills.join(", ")}`);

Expected Output:

Name: TypeScript, Age: 5
Learning: true
Skills: JavaScript, TypeScript

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