Node.js Executor

Run and test Node.js code directly in the browser.

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💡 Node.js Basics Guide

1. Declaring Variables and Constants

Use let or const for block-scoped variables. const is used for constants.

let x = 10;
const PI = 3.14;
let name = "Alice";
let isActive = true;

2. Conditionals (if / switch)

Use if, else if, else or switch for control flow.

let x = 2;
if (x === 1) {
  console.log("One");
} else if (x === 2) {
  console.log("Two");
} else {
  console.log("Other");
}

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

3. Loops

Use for, while, and forEach to iterate over data.

for (let i = 0; i < 3; i++) {
  console.log(i);
}

let n = 3;
while (n > 0) {
  console.log(n);
  n--;
}

4. Arrays

Use arrays to store ordered lists of values. Access them with indexes.

let fruits = ["apple", "banana", "cherry"];
console.log(fruits[0]);
console.log(fruits.length);

5. Array Manipulation

Use methods like push, pop, slice, and reverse.

fruits.push("kiwi");
fruits.pop();
console.log(fruits.slice(0, 2));
console.log(fruits.reverse());

let squares = [1, 2, 3, 4, 5].map(x => x * x);
console.log(squares);

6. Console Input/Output

Use console.log for output and readline module for input.

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question("What's your name? ", name => {
  console.log(`Hello, ${name}`);
  rl.close();
});

Node.js Basics Guide

7. Functions

Functions can be declared or expressed. Arrow functions are often used in modern JavaScript.

function greet(name) {
  return `Hello, ${name}`;
}

const add = (a, b) => a + b;

console.log(greet("Alice"));
console.log(add(2, 3));

8. Objects (Maps)

Objects store key-value pairs. They are similar to dictionaries or maps.

let person = { name: "Bob", age: 25 };
console.log(person.name);
console.log(person["age"]);

// ES6 Map
const map = new Map();
map.set("a", 1);
console.log(map.get("a"));

9. Exception Handling

Use try, catch, and finally to handle errors safely.

try {
  throw new Error("Something went wrong");
} catch (e) {
  console.log(e.message);
} finally {
  console.log("Cleanup if needed");
}

10. File I/O

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

const fs = require("fs");

fs.writeFileSync("test.txt", "Hello File");
const data = fs.readFileSync("test.txt", "utf8");
console.log(data);

11. String Manipulation

Use methods like trim(), toUpperCase(), replace(), and split().

let text = "  Hello World  ";
console.log(text.trim());
console.log(text.toUpperCase());
console.log(text.replace("Hello", "Hi"));
console.log(text.split(" "));

12. Classes & Objects

ES6+ supports OOP with class syntax.

class Person {
  constructor(name) {
    this.name = name;
  }
  greet() {
    return `Hi, I'm ${this.name}`;
  }
}

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

13. References

Objects and arrays in JavaScript are passed by reference.

function update(arr) {
  arr.push("changed");
}

let data = ["original"];
update(data);
console.log(data);  // ["original", "changed"]