undefined Keyword

In programming, the undefined keyword is used to represent a value that has not been assigned yet. It is different from null, which represents a value that has been explicitly assigned to be nothing.

How undefined is Used

The undefined keyword is often used in the following situations:

• When a variable is declared but not assigned a value
• When a function is called without arguments
• When an object property is accessed but does not exist

Examples of undefined

// Example 1: Variable declared but not assigned
let myVariable;
console.log(myVariable); // Output: undefined

// Example 2: Function called without arguments
function myFunction() {
  console.log(arguments); // Output: undefined
}
myFunction();

// Example 3: Object property accessed but does not exist
const myObject = {};
console.log(myObject.myProperty); // Output: undefined
  

Differences Between undefined and null

The undefined and null keywords are both used to represent values that are not defined, but there are some key differences between them:

• undefined is a primitive value, while null is an object.
• undefined is assigned to variables that have not been initialized, while null is assigned to variables that have been explicitly set to nothing.
• undefined is not equal to null, even though they both represent values that are not defined.

Conclusion

The undefined keyword is a useful tool for representing values that have not been assigned yet. It is important to understand the difference between undefined and null in order to use them correctly in your code.