Function scope is within the function.

Block scope is within curly brackets.

​

var character4 = 

function foo() {

    if(true) {

        var character1 = "Robin"      //function scope

        let character2 = "Ted"        //block scope

        const character3 = "Barney"   //block scope

    }

    console.log(character1)  //Robin

    console.log(character2)  //not defined

    console.log(character3). //not defined

}

//let

1. It's used in block-scoped.

2. It does not allow to redeclare variables.    

3. Hoisting does not occur in let.

// var 

1. It's used in function scoped.

2. It allows to redeclare variables.

3. Hoisting occurs in var.

var is function scoped and let is block scoped. Let's say you have:

function understanding_var() {

    if (1 == 1) {

        var x = 5;

        console.log('the value of x inside the if statement is ' + x);

    }

    console.log(x);

} 

//output: the value of x inside the if statement is 5

          5

​

function understanding_let() {

    if (1 == 1) {

        let x = 5;

        console.log('the value of x inside the if statement is ' + x);

    }

    console.log(x);

} 

//output: the value of x inside the if statement is 5

          Uncaught ReferenceError: x is not defined

var is defined throughout the entire function, even if it's inside the if 

statement, but the scope of let is always within the curly braces, not outside

it, even if the conditional statement is inside the function.

let: //only available inside the scope it's declared, like in "for" loop, 

var: //accessed outside the loop "for"

function run() {

  var foo = "Foo";

  let bar = "Bar";

​

  console.log(foo, bar);

​

  {

    let baz = "Bazz";

    console.log(baz);

  }

​

  console.log(baz); // ReferenceError

}

​

run();

let = 10 // accessable only in defined scope

var = 10 // accessable in the function it is declared in (global variable in a function)

/* DIFFERENCE BETWEEN LET AND VAR */

​

//LET EXAMPLE

{

  let a = 123;

};

​

console.log(a); // undefined

​

//VAR EXAMPLE

{

  var a = 123;

};

​

console.log(a); // 123

In simple words 'var' is function scoped and 'let' is block scoped

var makes a grobal variable

let makes a local variable