# Null and undefined in JavaScript

`Null` and `undefined` in javaScript seems the same but there is a significant difference between the two. In this article let us explore the similarities and differences between them.

## Undefined
  Undefined means `no-value`. if you have declared a variable but did not initialize/assign it with any value,By default it stays `undefined`, If you try to read a non-existing property in an object it gives `undefined`. you can also assign a variable as `undefined`.

```javascript
   let i;
   console.log(i); //undefined
   i={};
   console.log(i.something); //undefined
   i= undefined;
   console.log(i); //undefined
```


## Null
  Null is `non-existing value` or you can also say `no object value`.A variable becomes `null` only when you assign it as `null`. so `null` doesn't come by default.

```javascript 
   let i;
   console.log(i);// undefined
   i = null;
   console.log(i);// null
```

Both null and undefined evaluates to `falsy`.
```javascript
   let i; 
   if(i){
     console.log('truthy');
   }
   else{
     console.log('falsy');
    } //prints falsy
   i=null;
   if(i){
     console.log('truthy');
    }
   else{
     console.log('falsy');
    } // prints falsy
```
  as we can see both `null` and `undefined` evaluates to `falsy` values.

 But interestingly if we check the type of `null` it gives object even though 
 both `null` and `undefined` are said to be primitives. This is regarded as 
 mistake in javaScript implementation.
```javascript
   console.log(typeof null); //object
   conosle.log(typeof undefined); //undefined
```
Why `typeof null` gives `object` is explained in [this](https://v8.dev/blog/react-cliff) v8 article.  
![v8](https://cdn.hashnode.com/res/hashnode/image/upload/v1639296471054/sYtQCCsAa.svg+xml)

following the above image Brendan Eich the (creator of javascript) designed JavaScript to make typeof return 'object' for all values on the right-hand side. That’s why `typeof null` gives `object` despite the spec having a separate Null type.

one more thing is when we compare null and undefined with `===` it returns `false` but when we compare `null == undefined` it returns `true` because of type-coercion.

#### summarizing the post:
1. undefined means `not-defined`. a variable is `undefined` until you give it some value.
2. null means `no-value`. something becomes null only if it is made(assigned) null.
3. null and undefined both evaluate to falsy.
4. null and undefined both are primitive values.
5. `typeof null` gives `object`.


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