Understanding Undefined in JavaScript

In JavaScript, undefined is a primitive value that represents the absence of a value.
It is one of the two falsy values in JavaScript, along with null.

How undefined is Created

There are several ways that undefined can be created in JavaScript:

• When a variable is declared but not assigned a value
• When a function parameter is not passed an argument
• When an object property is accessed and the property does not exist
• When the return statement in a function is called without an argument

Checking for undefined

You can use the typeof operator to check if a value is undefined:

“`
const myVariable = undefined;

if (typeof myVariable === “undefined”) {
// Do something
}
“`

Comparison to null

undefined and null are both falsy values, but they are not the same.
null is a special value that represents an intentional absence of a value,
while undefined represents the absence of a value due to a lack of assignment or definition.

Conclusion

undefined is a fundamental concept in JavaScript.
It is important to understand how it is created and how to check for it in order to avoid errors in your code.
By using the typeof operator, you can ensure that your code handles undefined values appropriately.