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
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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.
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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