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JavaScript Fundamentals

Uploaded : 3 months ago Updated : 3 months ago beginner

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The building blocks of logic

You can store values. Now learn to act on them: functions, conditions and loops — the heart of every program.

Functions: reusable blocks

A function packages code you can call again and again, optionally with inputs (parameters) and a return value.

function add(a, b) {
  return a + b;
}
const arrow = (a, b) => a + b;  // same thing, shorter
add(2, 3); // 5

if (score >= 50) {
  console.log("Pass");
} else {
  console.log("Try again");
}

=== vs ==

Use strict equality === (and !==). It compares value AND type, avoiding surprising conversions.

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

const nums = [1, 2, 3];
nums.forEach(n => console.log(n));

Watch your scope

Variables declared with let/const live only inside their { } block. Reaching for one outside it is a common bug.

What is a callback?

A function passed to another function to run later — e.g. the arrow function inside forEach.

Arrow or regular function?

Arrow functions are shorter and keep the surrounding this. Use them for short callbacks.

What does return do?

It sends a value back to whoever called the function and ends the function.