Var, Let and Const

This blog consist the scope and use of var, let and const in Javascript. Three of the above methods are used to define a variable in Javascript but three of them hold a different properties and scope which vary their usage in a function.

Scope of Var

Scope means in simple language that where the particular variables can be used.

Var has a global scope. That means that any variable that is declared with var outside a function block can be used in the whole function.

// Example
var x = 1;

if (x == 1) {
  var x = 2;

  console.log(x);
  //Prints 2
}

console.log(x);
//Prints 2

Scope Of Let

Anything within {} is a block. So a variable declared in a block with the let is only used within that block.

// Example
let a = 10;
If(true){
	let a = 5;
	let b = 20;
	console.log(a); //Prints 5
	console.log(b); //Prints 20
}
console.log(a); //Prints 10
console.log(b); //Undefined

Scope of Const

Variables declared with the const maintain a fixed values.  const declarations share same similarities as let declarations.

Like let declarations, const declarations can only be used within the block it is declared.

// Example
var x = 10;
// Here x value is 10
{ 
    const x = 2;
    // Here x value is 2
}
// Here x value is 10