Undefined vs Null

Differences Between Undefined vs Null

In JavaScript, Variables are like a remote control that actually controls the object. If the remote control is not programmed to control any of the objects, it can be tagged as Undefined. On the other hand, if the remote control is programmed but not to do anything, it can be assigned to Null. Null is an assignment value; it can be assigned to a variable as a representation of no value. Undefined is a type itself, while null is an object. So Undefined is a special type, whereas Null is an object in JavaScript.

Below the JavaScript code snippet will give the output is undefined.

var x; console.log (x); ð  undefined

If someone checks the type of null, it will print the output as “object” as shown in the below JavaScript code snippet:

console.log (typeof null); ð  object

We can say that Undefined means a variable that has been declared, but the variable’s value has not yet been defined. Undefined is of type “undefined”, which can be checked from the below JavaScript code snippet:

var test; Console.log (typeof test); ð  undefined

One can also declare a variable and then assign “undefined” to it like below:

var test = undefined; Console.log (test); ð  undefined

Unassigned variables are initialized by JavaScript with a default value of undefined, whereas JavaScript never sets a value to null automatically; it must be done programmatically.

Head to Head Comparison Between Undefined and Null (Infographics)

Below is the top 8 comparison between Javascript Undefined and Null:

Key Differences Between Javascript Undefined and Null

Let us discuss some of the major Differences Between Undefined and Null:

1. Undefined means a variable has been declared but not yet been assigned a value.
2. “null” is an assignment value that means “no value”.
3. “undefined” and “null” both are primitives.
4. “undefined” is of type undefined.
5. “null” is of type object.
6. JavaScript never set a value to “null”; programmers use it to indicate that a “var” has no value.
7. JavaScript set an unassigned variable with a default value of “undefined”.
8. “undefined” is not a valid value in JSON (JavaScript Object Notation), whereas “null” is a valid value in JSON.
9. One can check if a variable is undefined using: type of variable === “undefined.”
10. Way to check if a variable is null using :                                                                                                                        variable === null
11. Equality operator will treat them as equal whereas Identity operator won’t treat them as equal.                        null === undefined //false                                                                                                                                                    null == undefined //true
12. The value “null” represents the intentional absence of any object value. It is one of JavaScript’s primitive values.
13. Null is written with a literal: “null”. It is not an identifier for a global object’s property like “undefined” can be. “null” gives the lack of identification, means that a variable point to no object.
14. “undefined” is a global variable that JavaScript creates at runtime.
15. When one performs arithmetic conversion on “null”, value determined is 0, this conversion can be verified:      var v1 = 3+null;                                                                                                                                                                console.log (v1); //3
16. “undefined” does not carry out arithmetic conversion like “null” does; if we try to add it to a numeral, you will get NaN (Not-a-Number) error.

Comparison Table Undefined and Null

Below is the list of points; describe the comparison Between Javascript Undefined and Null.

BASIS of Comparison Between Undefined vs Null	Undefined	Null
Definition	Variable has been declared but not yet been assigned a value	assignment value that means “no value.”
Type	Undefined	Object
JSON	Invalid	Valid
Nature	Variable declared but not yet assigned	Represent intentional absence of object value
Check	typeof variableName === “undefined”	variableName === null
Arithmetic	Not-a-number (NaN) error	treated as zero value
Comparison	Equality operator will return true	Identity operator will return false
Identifier	Can be an identifier for a property of a global object	Not an identifier for a property of the global object

Conclusion

Most of the time, people misunderstand the difference between Undefined vs Null. If the distinction between Undefined vs Null remains unclear, it can lead to certain test cases issues.

A variable can be said to be “undefined” if it is declared, but no value has been given to it. On the other hand, “null” is a value assigned to a variable and represents “no value”. Therefore “undefined” is a variable type, where “null” is an object value.

“null” is considered as a place-holder for nothing. It means we have intentionally assigned a value to a variable and thus assuming the value of nothing to a variable. When checking for null or undefined, one needs to be aware of equality (==) and identity (===) operators, as former perform type conversion.

typeof null   //object type of undefined   // undefined null === undefined    //false null == undefined   //true null == null   //true null === null   //true !null   //true isNaN ( 1 + null )   //false isNaN ( 1 + undefined )   //true

So, when it comes to the difference in type, “null” is an object with a valid value having no properties, is non-mutable, and a single instance exists in the system all the time. One can verify the nature of “null” by using the “type of” operator. The use of this operator will give the output as “object”. If we use the “type of” operator on an object that belongs to all criterion of an undefined list, we will receive object type as “undefined”.

Another major difference between Undefined vs Null can be concluded with conversion to primitive types. The way both are converted to primitive types is the key area for differentiation. While performing the arithmetic conversion on “null”, the value determined is zero. However, “undefined” does not carry such conversion. If we try to add “undefined” to a numeral, you will get a Not-a-number error.

Usage of “null” can be very handy in the real world scenario. For example – Some people don’t have a middle name. So, in this case, it is better to assign a value null to a middle name variable in a person object. If someone is accessing the middle name variable in person object and it has value “undefined”. There is no way to ascertain that the developer forgot to initialize this variable or did not have any value. If it is assigned as null, it means a user can easily infer that the middle name variable does not have any value.

So, to summarize, “null” and “undefined” have different meanings. While “null” is a special keyword that indicates an absence of a value, “undefined” means “it does not exist”. There are situations when it helps to differentiate “a value of null” and “no value”. When sending updates for a list, “null” may mean replace this field with “null”, and undefined may mean “do not touch”. When dealing with default function parameters: undefined means “use default value” and null means “use null”. Having Undefined vs Null as two distinct things in JavaScript can be honestly painful; however, if one is a JavaScript developer, he/she might like it.

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