Learn JavaScript: a Beginner Tutorial

Follow these lessons in order. Each one has a short explanation and code you can run instantly in My Compiler.

Lesson 1: Hello, World!
Every language starts here: print a message to the screen to check that everything works.
```
console.log("Hello, World!");
```
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Lesson 2: Variables
Variables store values such as text, whole numbers and decimals so you can reuse them.
```
const name = "Ada";
let age = 21;
const height = 1.75;
console.log(name, age, height);
```
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Lesson 3: Conditions

if / else lets your program choose a path depending on a value.

const age = 18;
if (age >= 18) {
  console.log("Adult");
} else if (age >= 13) {
  console.log("Teenager");
} else {
  console.log("Child");
}

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Lesson 4: Loops
Loops repeat a block of code: use for when you know the count and while when you wait for a condition.
```
for (let i = 1; i <= 5; i++) {
  console.log(i);
}

let n = 3;
while (n > 0) {
  console.log("Countdown", n--);
}
```
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Lesson 5: Functions
A function packs code into a reusable block that takes inputs and returns a result.
```
function add(a, b) {
  return a + b;
}

console.log(add(2, 3));
```
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Lesson 6: Fibonacci sequence

Each number is the sum of the two before it. A classic exercise that combines variables, loops and arithmetic.

function fib(n) {
  let a = 0, b = 1;
  const out = [];
  for (let i = 0; i < n; i++) {
    out.push(a);
    [a, b] = [b, a + b];
  }
  console.log(out.join(" "));
}

fib(10);

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