TypeScript Syntax

Basic Structure

TypeScript extends JavaScript and uses the .ts file extension. A typical file includes import statements, type annotations, interfaces, classes, and functions.

Output:

Variable Declarations

You can declare variables with let, const, or var. Always preferlet and const for block scoping. Type annotations can be included:

let count: number = 10;
const username: string = "Alice";

function greet(name?: string): void {
  if (name) {
    console.log("Hello, " + name);
  } else {
    console.log("Hello, Guest");
  }
}

Function Syntax

Functions can define the types of their parameters and return values. Parameters can be optional using?:

function add(a: number, b: number): number {
  return a + b;
}

const logMessage = (message: string): void => {
  console.log(message);
}

Type Annotations

Type annotations let you declare expected types for variables, function parameters, and return values:

let isActive: boolean = true;
let score: number = 100;
let tags: string[] = ["code", "typescript"];

Comments

Use // for single-line and /* ... */ for multi-line comments:

// This is a single-line comment

/* This is
   a multi-line comment */

Compatibility

TypeScript code must be compiled into JavaScript using the TypeScript Compiler (tsc). This makes it runnable in any browser or JavaScript environment.

tsc script.ts

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