Javascript : null & undefined

In JavaScript, null is a value that represents the intentional absence of any

object value. It is technically a primitive type, although in some cases

it behaves as an object.

undefined means the variable has not been assigned a value yet.

Checking for null:

You can check whether a value is null using the === operator:

Code:

var s= null;

if(s===null){

console.log('s is null')

}

Output:

s is null

If variable 's' is null or undefined then == return true.

Code:

if(s==null){

console.log('s is null or undefined')

}

Output:

s is null or undefined

null vs undefined:

undefined means the variable has not been assigned a value yet,

whereas null means the variable has been explicitly defined as null

null & undefined together termed as nullish value.

Nullish value vs Non-nullish value:

Nullish values are different from non-nullish values in that

nullish values throw a TypeError when you try to access one of

their properties, whereas non-nullish values do not.

Code:

let v = 42;

console.log(v.test); // undefined

v = null;

v.test; // Throws `TypeError: Cannot read property 'test' of null`

v = undefined;

v.test; // Throws `TypeError: Cannot read property 'test' of undefined`

Arithmetic Operations on null:

During mathematical operation javaScript converts null to 0.

consider following code.

Code:

console.log(2 + null); // 2

console.log(null + 2); // 2

console.log(2 - null); // 2

console.log(null - 2); // -2

console.log(2 * null); // 0

console.log(null * 2); // 0

console.log(2 ** null); // 1

console.log(0 ** 2); // 0

console.log(null / 2); // 0

Output:

2

2

2

-2

0

0

1

0

0

Arithmetic Operation on undefined:

Result of any arithmetic operation on undefined is always NaN.

Code:

console.log(2 + undefined); // NaN

console.log(2 * undefined); // NaN

console.log(2 - undefined); // NaN

console.log(2 ** undefined); // NaN

console.log(2 / undefined); // NaN

console.log(undefined + 2); // NaN

console.log(undefined - 2); // NaN

console.log(undefined * 2); // NaN

console.log(undefined / 2); // NaN

console.log(undefined ** 2); // NaN

Output:

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

Applying typeof operator on null

Code:

var s = null

console.log(typeof s)

Output:

object

Why typeof null is an object?

It was a historial mistake.In the early versions of JavaScript, the

language used a 32-bit system to store values. These bits were divided

into two parts: the type tag and the data value.The type tag for objects

was 000, which corresponds to the binary value 000 in the least significant

bits.The type tag for null was also 000,leading to the confusion and the

typeof null returning "object".

Checking if variable is not null but object:

Code:

function isObject(v) {

return typeof v === "object" && v !== null;

}

var t = {

name: "sangram",

};

if(isObject(t)){

console.log('t is object')

}

var s = null

if(!isObject(s)){

console.log('s is not an object')

}

Output:

t is object

s is not an object

Explanation:

1)isObject() function return true if passed variable has not null value &

it's type is object.

2)isObject() function return false if passed variable has null value or

it's type not object.

Applying typeof operator on null

Code:

var t = undefined

console.log(typeof t)

Output:

undefined

Concatenation:

when we concat a variable with null value or variable with undefined value,

first toString() method is called on this variables.toString() for variable

with null value is 'null' string.toString() for variable with undefined

value is 'undefined' string.

string concatenation on null:

Code:

var s = null

console.log(s+ 'some value')

console.log('some value' + s)

Output:

nullsome value

some valuenull

string concatenation on undefined:

Code:

var s = undefined

console.log('some value' + s)

console.log(s + 'some value')

Output:

some valueundefined

undefinedsome value

Comparing two null variables:

Code:

var s =null;

var t =null;

if(s===t){

console.log("Equal")

}else{

console.log("Not Equal")

}

Output:

Equal

Comparing two undefined variables:

Code:

var s =undefined;

var t =undefined;

if(s===t){

console.log("Equal")

}else{

console.log("Not Equal")

}

Output:

Equal