What happens when you don’t declare a variable in Javascript?

• If you don’t explicitly declare a variable, you risk creating an implied global variable. This is a problem, as you will be unable to create multiple instances of that object, as each new instance will overwrite the data from the last.
• In general, global variables should be used only in very specific situations and are typically not recommended, as they can lead to a lot of odd side effects that may be difficult to track down.