Scope of var and let in JavaScript

Var

The variable statement declares a variable, optionally initializing it to a value - MDN web docs

Let

Let is the new keyword introduced in ES6.

The let statement declares a block scope local variable, optionally initializing it to a value - MDN web docs

var a = 'a';

function foo() {
    console.log(a);//a
    
    let b = 'b';
    console.log(b);//b
    
    var c = 'c';
    console.log(c);//c

    if (c === 'c') {
        let d = 'd';
        console.log(d);//d
        
        var e = 'e';
        console.log(e);//e
        
        {
            let f = 'f';
            console.log(f)//f
        }
        //console.log(f)//ReferenceError: f is not defined
    }
    //console.log(d);//Uncaught ReferenceError: d is not defined

    console.log(e);//e
}

foo();

console.log(a);

//console.log(b);//Uncaught ReferenceError: b is not defined

//console.log(c);//ReferenceError: c is not defined

Based on the above code snippet the following are the behaviours when variable are created using var and let keywords

• Any variable created with var keyword inside a function is not accessible outside the function
• Function can access variables (var or let) which are outside the function
• Varibles created with let keyword is accessible only within the block {}