In the JAVASCRIPT, the variables can be used before declared, this kinds of mechanism is called Hoisted. It's a default behavior of JavaScript.

You can EASILY understanding in the below example in detail.

//The variable declaration LOOK like.
var emp;
//The variable INITIALIZATION look like.
emp = "Anil Singh";
var emp; //The declaration of emp is hoisted but the value of emp is undefined.
emp = 10; //The Assignment still occurs where we intended (The value of emp is 10)
function getEmp() {

var emp; //The declaration of a different variable name emp is hoisted but the value of emp is undefined.

console.log(emp); //The output is undefined
emp = 20; //The assignment values is 20.
console.log(emp); //The output is 20.
}
getEmp();
console.log(emp); //The variable named emp in the outer scope still CONTAINS 10.

In the JavaScript, the variables can be used before declared, this kinds of mechanism is called Hoisted. It's a default behavior of JavaScript.

You can easily understanding in the below example in detail.

//The variable declaration look like.
var emp;
//The variable initialization look like.
emp = "Anil Singh";
var emp; //The declaration of emp is hoisted but the value of emp is undefined.
emp = 10; //The Assignment still occurs where we intended (The value of emp is 10)
function getEmp() {

var emp; //The declaration of a different variable name emp is hoisted but the value of emp is undefined.

console.log(emp); //The output is undefined
emp = 20; //The assignment values is 20.
console.log(emp); //The output is 20.
}
getEmp();
console.log(emp); //The variable named emp in the outer scope still contains 10.