What is Undefined in JavaScript?

In JavaScript, the undefined value is a primitive value that represents the absence of a value.

How is Undefined Created?

Undefined can be created in several ways:

• When a variable is declared but not assigned a value.
• When a function is called without passing arguments to parameters that do not have default values.
• When a property of an object is accessed that does not exist.

Checking for Undefined

To check if a value is undefined, you can use the typeof operator. The typeof operator returns a string that indicates the type of the value. For undefined, the typeof operator returns the string “undefined”.


const myVariable;
console.log(typeof myVariable); // Output: undefined


Comparison to Null

Undefined is often confused with null, but they are not the same. Null is a primitive value that represents the intentional absence of a value, while undefined represents the absence of a value due to the lack of initialization or assignment.

Conclusion

Undefined is an important concept in JavaScript that represents the absence of a value. It is created in various scenarios and can be checked using the typeof operator. Understanding the difference between undefined and null is crucial for effective JavaScript programming.