TypeScript CLI Runner Online

Quickly test TypeScript code in a command-line-like environment—perfect for developers on the go.

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📚 Everyone's learning Typescript – what about you?

💡 TypeScript Basics Guide for Beginners

1. Declaring Variables

TypeScript allows static typing with let, const, and type annotations.

let x: number = 10;
const pi: number = 3.14;
let name: string = "Alice";
let isActive: boolean = true;

2. Conditionals (if / switch)

Use if, else if, and else for branching. switch handles multiple values.

let x = 5;
if (x > 0) {
  console.log("Positive");
} else if (x < 0) {
  console.log("Negative");
} else {
  console.log("Zero");
}

switch (x) {
  case 1:
    console.log("One");
    break;
  case 2:
    console.log("Two");
    break;
  default:
    console.log("Other");
}

3. Loops

Use for, while, and for...of for iteration.

for (let i = 1; i <= 5; i++) {
  console.log(i);
}

let i = 5;
while (i > 0) {
  console.log(i);
  i--;
}

4. Arrays

Use square brackets [] to define arrays.

let numbers: number[] = [1, 2, 3, 4, 5];
let names: string[] = ["Alice", "Bob"];
console.log(numbers[1]);

5. Array Manipulation

Use built-in methods like push, splice, and filter.

let arr = [10, 20, 30];
arr.push(40);          // Append
arr.splice(1, 1);      // Remove second element
console.log(arr);

6. Console Input/Output

Use console.log to display output in the console.

const name: string = "Alice";
console.log("Hello, " + name);

7. Functions

Declare functions with typed parameters and return values.

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

console.log(add(3, 5));

8. Maps

Use plain objects or Map for key-value structures.

const m = new Map<string, number>();
m.set("Alice", 25);
console.log(m.get("Alice"));

9. Exception Handling

Use try and catch to handle errors.

try {
  throw new Error("Something went wrong");
} catch (e) {
  console.error(e.message);
}

10. File I/O (Node.js only)

Use Node.js fs module to read and write files.

import * as fs from "fs";

fs.writeFileSync("file.txt", "Hello File");
const content = fs.readFileSync("file.txt", "utf-8");
console.log(content);

11. String Manipulation

Use string methods like length, concat, includes.

let str = "Hello World";
console.log(str.length);
console.log(str + "!");
console.log(str.includes("World"));

12. Classes & Objects

TypeScript supports object-oriented programming.

class Person {
  name: string;
  constructor(name: string) {
    this.name = name;
  }
  greet() {
    console.log(\`Hi, I'm \${this.name}\`);
  }
}

const p = new Person("Alice");
p.greet();