var:
If we use var outside of a function, it belongs to the global scope.
If we use var inside of a function, it belongs to that function.
Example:
var iData = "This is Global Data";
function myFunction() {
var iFuncData = "This data scope within function i.e, myFunction";
}
console.log(iData);
//Output: This is Global Data
console.log(iFuncData);
//Output: 'iFuncData' is undefined
let:
let is the block scoped version of var, and is limited to the block (or expression) where it is defined.
If we use let inside of a block, i.e. a for loop, the variable is only available inside of that loop.
Example:
let iData = 2.5;
const:
const is a variable that once it has been created, its value can never change.
Example:
const iData = 2.5;
