As a javascript devloper. We all Know about let,const, var , keywords are used to declared variable and assign a value , In this article i am talking about difference between these keywords.

Before Moving to this Topic , we know about term block

Block is nothing but anything inside curly bracket which is "{ }" called block

Basically there are three type of scope

• Global scope

• Function scope

• Local scope

var, let, const works around this three scope, let's understand better with the help of example

- let's see the behavior of var, let, and const keywords in the local scope variable declared inside the scope called local scope .

Lets take example

{
    let  name  = 'fuzz ';
    const class = 11;
    var age = 23;
}

console.log(name); // Uncaught ReferenceError: name is not defined
console.log(class);  // Uncaught ReferenceError: class is not defined
console.log(age);  // 23

in the above example , let ,const are giving error and var return value so here we have see var is acess globally , we discuss further about it . so always prefer let and const keyword inside block scope which is local scope . it means let and const is local scope

Lets see how these js variables works inside function scope

• variables inside the function scope using let, var, and const keywords are not accessed outside the function. it gives error

lets take example of function scope

// student() is a function

function student() {
 let name = "peter";
 const id = 007;
 var age = 23;   
}

student();

console.log(name); // Uncaught ReferenceError: name is not defined
console.log(id);  // Uncaught ReferenceError: id is not defined
console.log(age);  // Uncaught ReferenceError: age is not defined

As you saw in the above example, all variables return errors while executing outside the function. not even var keyword . so the variable declared with the var keyword is function scope

- global scope

variable acess outside the block and function we call global scope.

exapmle

let name = "guffy";
 const id = 101;
 var age = 23;  

// student() is a function

function student() {
  console.log(name); // guffy
  console.log(id);  // 101
  console.log(age);  // 23
}

student ();

console.log(name); // guffy
console.log(id);  // 101
console.log(age);  // 23

conclusion

• Var keywords is function scope

• Let is block scope

• const is block scope

Here in above Example . all variables acess anypart from the javascript program.

• More difference of let const and var keywords **

• in the var keyword we can reassign the value, so it is updated and redeclared

• in let case, we can also reassign the value ,so its is updated but not redeclared

• in const case, we can never reassign the value, so neither be updated and nor be redeclared

• when we try to execute a variable before declaration , using var keyword in this case it gives an undefined error.

• when we try to execute the variable before declaration then in the let and const case its gives a reference error.

That's all. It would be really helpful if you give feedback about this article .Thank you

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