var vs let vs const

Old habits die hard. This applies to me when it comes to declaring variables especially when I get in the flow and I am just automatically declaring all variables with var. So the purpose of this article is for me to stop this habit once for all.

Var is function scope. This means when a variable is declared with a var in a function, that variable can’t be accessed outside of that function and it will throw an error.

function sound() {
    var dog = "woof"
    console.log(dog) 
}
sound()
/// woof
woof
/// Uncaught ReferenceError: dog is not defined

However, if a variable is declared with a var in a block scope, that variable can be accessed outside of that block scope.

var sound = "woof"
if (sound === "woof") {
 var animal = "dog"
 console.log(`${animal} goes ${sound}`)
}
/// dog goes woof
animal
/// "dog"

This problem can be fixed by declaring variables with let, which is block scoped.

var sound = "woof"
if (sound === "woof") {
 let animal = "dog"
 console.log(`${animal} goes ${sound}`)
}
/// dog goes woof
animal
/// Uncaught ReferenceError: animal is not defined

Const is similar to let but with one big difference. Const can’t be reassigned. Also both const and let can’t be redeclared unlike var.