declare

You can declare using let , var, or const. Additionally, you can also implicitly declare without using any of these keywords. Implicit variables are also global variables, but can be prevented in strict mode. Read on hoisting to clear more confusions that arise due to declaration.

Note

use strict; solves a lot of problem by eliminating implicit declaration

In terms of scope, these are the differences:

• var has function scope
• let has block scope
• const has block scope

var x = 14
let foo = "bar"
const pi = 3.14
 
// Implicit
tuna = "tuni"

Common confusion

const doesn’t allow re-assignment. But it does allow changing individual elements.

const array = [1,2,3,4,5,6,6,6]
 
array[0] = 10 // allowed
 
array = [4,2,0] // ERROR, not allowed