Difference Between null and undefined in JavaScript

null is an assigned value. It means nothing. undefined means a variable has been declared but not defined yet. null is an object.

1. What is difference between null and undefined in JavaScript with example?
2. Why null == undefined is true?
3. Why JavaScript has null and undefined?
4. Should I use null or undefined JavaScript?
5. Is null == undefined?
6. Is null undefined?
7. Is NaN and null same?
8. Is NaN equal to null?
9. Is NaN null Python?
10. Should I return null or undefined?
11. Why do I get undefined JavaScript?
12. What is typeof undefined?

What is difference between null and undefined in JavaScript with example?

In JavaScript, undefined is a type, whereas null an object. It means a variable declared, but no value has been assigned a value. Whereas, null in JavaScript is an assignment value. You can assign it to a variable.

Why null == undefined is true?

null and undefined both return false . That's why your code is actually checking if false is equal to false . However their types are not equal. Because of that, the next statement will return false, as the === comparison operator checks both the types and their value.

Why JavaScript has null and undefined?

Undefined is supposed to mean a variable has no value (or a property does not exist) because the programmer has not yet assigned it a value (or created the property). Null is supposed to signal that a variable has no value because the programmer purposefully cleared the value and set it to `null`.

Should I use null or undefined JavaScript?

Only use null if you explicitly want to denote the value of a variable as having "no value". As @com2gz states: null is used to define something programmatically empty. undefined is meant to say that the reference is not existing. A null value has a defined reference to "nothing".

Is null == undefined?

undefined means a variable has been declared but not defined yet. null is an object. undefined is of type undefined .

Is null undefined?

null is an assigned value. It means nothing. undefined typically means a variable has been declared but not defined yet.

Is NaN and null same?

null values represents "no value" or "nothing", it's not even an empty string or zero. It can be used to represent that nothing useful exists. NaN stands for "Not a Number", it's usually the result of a mathematical operation that doesn't make sense, e.g. 0.0/0.0 .

Is NaN equal to null?

null and undefined are loosely equal to each other but are strictly not equal to each other. NaN is a result of nonsensical computation which cannot produce a meaningful result. NaN is the only value which isn't equal to itself.

Is NaN null Python?

When it comes to data wrangling, dealing with missing values is an inevitable task. Unlike other popular programming languages, such as Java and C++, Python does not use the NULL keyword. Instead, Python uses NaN and None .

Should I return null or undefined?

Undefined typically refers to something which has not yet been assigned a value (yet). Null refers to something which definitively has no value. In that case, I would recommend returning a null. Note that a function with no specified return value implicitly returns undefined.

Why do I get undefined JavaScript?

A variable that has not been assigned a value is of type undefined . A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned .

What is typeof undefined?

An undefined value in JavaScript is pretty common — it means a variable name has been reserved, but no value has been assigned to that reference yet. ... The typeof undefined is the string "undefined" — and undefined is a falsy value that is loosely equal to null but not to other falsy values.