Declaring variables

Learn to declare variables with let, const and var and the basic differences between them.

What is a variable?

A variable is a name you give to a value. You can later use this name to read the value, change it or print it on screen. In JavaScript a variable is declared with the let, const or var keyword.

The most common one is let. To assign a value to a let variable you use the = sign: let sehir = "Berlin";. Here sehir is the variable's name and "Berlin" is its value.

Declaring with const

A variable declared with const gets its value once and cannot be reassigned later. When you are sure a value will never change, it is a good habit to use const.

For example you write const pi = 3.14;; if you later write pi = 3.15; JavaScript throws a TypeError. This protects you from changing a constant by mistake.

Printing with console.log

To see the value of a variable you declared, you use console.log(). You put the variable's name inside the parentheses; JavaScript prints that variable's value to the console.

For example, write let yas = 30; and below it console.log(yas);; the console shows 30. console.log is a function; we will cover functions in detail later, for now just use it to print values.

Exercise Declare a variable and print it

Declare a sehir variable and give it a city name. Then print its value with console.log.

Show example solution

let sehir = "Berlin";
console.log(sehir);

Test yourself

Which of these variable declarations is valid?
- let 1sayi = 5;
- let sehir = "Berlin";
- let sehir = Berlin;
- let = "Berlin";
Show answer

let sehir = "Berlin"; — Correct. After let comes a name, then = and the value.
Declare a city variable with let
```
____
```
Show answer
```
let sehir = "Berlin";
```
Match each keyword to its role

let

Value can change
const

Cannot be reassigned
var

Old style, best avoided
console.log

Prints a value

Next lesson: Difference between const and let

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