Variables and Equality

Scope

There are two types of scope: block scope and module scope. Variables declared in a block can be accessed within that block. Variables cannot be redeclared in a block but can be shadow a declaration from a higher scope. Variables declared at the top level have module scope.

Variable Declaration

Variables can be declared using let or const. Variables declared as const cannot be reassigned.

const VERSION_STRING = '1.0.0' 

Variables can also be declared using 'destructuring declaration'

let point = {x:1, y:2}
let {x,y} = point // x is 1 and y is 2

Equality and Strict Equality

Variables can be tested for equality and strict equality using the == and === operators. Two values are strictly equal if they are equal and:

• They have the same type. So 1 and 1.0 are not strictly equal
• -0.0 and 0.0 are not strictly equal but NaN and NaN are