isNaN funtion and NaN error in Javascript

This blog post is dedicated to JavaScript newbie and JavaScript lover.

NaN is a "Not a Number" in JavaScript.

1. NaN error
- NaN error is very common for JavaScript developer. When you are looking some calculation that time generally come.

- One thing remember when you are working with JavaScript  and declare any variable (var i;) and that variable value default as 'undefined'. so its a good practice to assign default value to the variable.

//var first = undefined;
var first;

//So when you do console.log(first); its print in console 'undefined'
console.log(first);

So take care it and don't forget to assign default value to variable else it will create a problem on some statement.

var first = 0;

consol.log(first)
//Console output is 0

When getting NaN error?
- When variable value is undefined and use that variable and calculate with some other variable that time getting NaN.

Let's see example.

var first;
var second = 4;

console.log(first + second);
//Output is NaN

//As we prevent NaN, declare variable with default value
//in our case first variable value is undefined so let assign value to variable.

first = 0;
console.log(first + second);
//Output is 4

2. isNaN function
  - It's a global function in JavaScript to check if a value is a NaN value.

When you writing JavaScript code for calculation of numeric values and its a safe way to handle numeric value and check value is not a NaN value using IsNaN function.

Let's see example how to handle NaN value in JavaScript.

var first;
var second = 4;
var sum = first + second
if (isNaN(sum)){
  console.log("value is a NaN");
}else{
  console.log('Value is not a NaN');
}

Hope this is useful for newbie of JavaScript.