In JavaScript, null
and undefined
are two special values that represent the absence of a value. null
is used to explicitly indicate that a variable does not refer to any object, while undefined
is used to indicate that a variable has not been assigned a value.
Null
The null
value is a primitive value that represents the absence of an object. It is often used to indicate that a variable does not refer to any object. For example, the following code creates a variable called myObject
and assigns it the null
value:
var myObject = null;
The myObject
variable now does not refer to any object. If you try to access the myObject
variable, you will get an error.
Undefined
The undefined
value is a primitive value that represents the absence of a value. It is often used to indicate that a variable has not been assigned a value. For example, the following code declares a variable called myOtherObject
but does not assign it a value:
var myOtherObject;
The myOtherObject
variable now has an undefined
value. If you try to access the myOtherObject
variable, you will get an error.
Differences between null
and undefined
There are a few key differences between null
and undefined
:
null
is a primitive value, whileundefined
is a type itself.null
can be assigned to a variable, whileundefined
cannot.null
is converted to zero (0) while performing primitive operations, whileundefined
is converted to NaN while performing primitive operations.
When to use null
and undefined
In general, you should use null
to explicitly indicate that a variable does not refer to any object. You should use undefined
to indicate that a variable has not been assigned a value.
Here are some examples of when you might use null
:
To indicate that a user has not selected a value from a dropdown list.
To indicate that a function has not returned a value.
To indicate that an object does not have a particular property.
Here are some examples of when you might use undefined
:
To declare a variable that you will assign a value to later.
To access a property of an object that you know does not exist.
To indicate that a function has not been called.
Conclusion
null
and undefined
are two special values that represent the absence of a value in JavaScript. null
is used to explicitly indicate that a variable does not refer to any object, while undefined
is used to indicate that a variable has not been assigned a value. You should use null
to explicitly indicate that a variable does not refer to any object, and you should use undefined
to indicate that a variable has not been assigned a value.