What is undefined?
Undefined is a term used to describe a variable or function that has been declared, but hasn't been assigned a value yet. It is a special keyword that is used in programming to indicate that a variable or function has not yet been given a value.
What happens when you use undefined?
When a variable or function is declared without a value, it is given the value "undefined". This means that when you try to access the variable or function, it will return the value "undefined". This can be useful for debugging code, as it indicates that something is wrong with the code.
How to handle undefined?
When dealing with undefined values, it is important to check for them and handle them appropriately. You can do this by using the typeof operator to check for the value "undefined". If the value is undefined, you can then handle it how you want. For example, you may want to assign a default value to the variable instead.
Conclusion
Undefined is an important concept in programming that can be used to help debug code. It is important to check for undefined values and handle them appropriately, as they can cause unexpected behaviour in your code.