Top companies Node Js Interview questions 1

1) Difference between var, let, and const?

VAR

var msg = "Hello world";

if(true){
    console.log("1 "+ msg)
}
console.log("2 "+ msg)

// output
// 1 Hello world
// 2 Hellow world

“var” is globally accessible, even if it is inside the scope like below example

if(true){
    var msg = "Hello world";
    console.log("1 "+ msg)
}
console.log("2 "+ msg)

// output
// 1 Hello world
// 2 Hellow world

Above both “var” declaration gives output same.

LET

But “let” variable type will not accessible from one to another.

if(true){
    let msg = "Hello world";
    console.log("1 "+ msg)
}
console.log("2 "+ msg)
//  msg is not defined

Here the above example will give the output “msg is not defined”.

console.log("2 "+ msg)
                  ^

ReferenceError: msg is not defined
    at Object.<anonymous>

CONST

const msg = "Hello";
if(true){
    msg = msg + " world";
    console.log("1 "+ msg)
}
console.log("2 "+ msg)

const stands for constant.
The constant variable will not able to modify the values. So, it throws an error “type error” like below.

    msg = msg + " world";
        ^

TypeError: Assignment to constant variable.
    at Object.<anonymous>
var Globally Accessable on both inside and outside of scope
let Not Globally Accessable. It is accessable only in inside of scope
const Not Globally Accessable on both inside and outside of scope. Once declare and assign the variable will not able to modify the values.

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