Variables

Names you give to values so the program can remember them.

A variable is a name attached to a value. Think of it as a labeled box: you put something in, and later you can ask for whatever is inside by saying its name.

Declaring a variable

In modern JavaScript there are two keywords you'll use:

let age = 30;
const name = "Ada";

• let for values that might change.
• const for values that should not change (prefer this when you can).

You'll also see var in old code. Don't use it let and const behave better in almost every case.

Changing a value

let score = 0;
score = score + 10;
console.log(score); // 10

Trying to reassign a const is an error:

const pi = 3.14159;
pi = 3; // TypeError: Assignment to constant variable.

Naming rules

• Start with a letter, _, or $.
• No spaces. Use camelCase: userName, totalScore.
• Names are case-sensitive: count and Count are different variables.

A quick exercise

Try this in your console:

const greeting = "Hello";
const target = "world";
console.log(greeting + ", " + target + "!");

What gets printed? Now change target to your own name and run it again.

Next up: making decisions with if.