When using null in arithmetic operations, it will be converted to 0 implicitly. Using a undefined value in an arithmetic operation will result in NaN. Null is explicitly assigned to variables to indicate the absence of a value. Undefined is the value assigned to a variable when it’s declared but not assigned a value. Let’s look at a small table to solidify our understanding of the differences between the two, undefined

Null is usually used to represent missing values when dealing with variables related to a database or API.

On the other hand, the null value represents an object that is not available.

In JavaScript, variables that have not been defined or have been assigned an empty value are treated as undefined.

Now that we understand what is undefined, let us look at some key differences between undefined and null since they are often misunderstood as being the same. So ultimately, the value testVar turned out to be undefined. In this case, we initially set the value of the variable testVar to 20, but then we assigned its value to be undefined. By default, it gets the value (testVar) // undefined Code language: JavaScript ( javascript ) The following example declares the variable num. The following are some of the instances where a variable gets the value undefined Uninitialized variableĮvery JavaScript variable that we create without assigning any value gets the value of undefined. JavaScript explicitly sets the value undefined when we do not provide any value. The ECMA specifications define undefined as “the primitive value used when a variable has not been assigned a value”. The value undefined means we do not know its value.

The null value means we know that it does not have any value. Undefined is different from the value null.

Undefined also means non-existing property of an object or non-existing array element etc. It is an unintentional absence of any value. whenever we do not explicitly assign a value to a variable, JavaScript assigns the undefined value to it. Undefined is a primitive value that indicates that the value is not assigned. When we refer to undefined in JavaScript, it could be one of the following The return value of functions that don’t return a value.

Function argument that has not been supplied.

Javascript undefined