## What is undefined?
In programming, undefined is a special value that indicates that a variable has not been assigned a value yet. It is different from null, which is a value that represents the intentional absence of a value.
Undefined is often used to initialize variables that will be assigned a value later in the program. For example, the following code initializes the variable `x` to undefined:
“`
var x;
“`
This code will not cause an error, but if you try to access the value of `x` before it has been assigned a value, you will get an error.
### How to check if a variable is undefined
You can use the `typeof` operator to check if a variable is undefined. The `typeof` operator returns a string that indicates the type of the variable. For example, the following code will return “undefined”:
“`
console.log(typeof x);
“`
### How to handle undefined variables
There are a few ways to handle undefined variables. One way is to use the `if` statement to check if a variable is undefined before you try to access its value. For example, the following code will only log the value of `x` if it is not undefined:
“`
if (x !== undefined) {
console.log(x);
}
“`
Another way to handle undefined variables is to use the `||` operator. The `||` operator returns the first truthy value in its operands. For example, the following code will log the value of `x` if it is not undefined, otherwise it will log the value of `y`:
“`
console.log(x || y);
“`
### Conclusion
Undefined is a special value that indicates that a variable has not been assigned a value yet. It is important to handle undefined variables carefully to avoid errors.