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Why Promises?
Promises are the cleanest (but not the only) way to handle the common scenario where we need to make requests to a server, which is typically done via an HTTP request. JavaScript's built-in fetch() function (that we'll cover in a later course) returns a promise.
I/O, or “input/output”
Almost every time you use a promise it will be to handle some form of I/O. I/O, or input/output, refers to when our code needs to interact with systems outside of the (relatively) simple world of local variables and functions.
Common examples of I/O include:
- HTTP requests
- Reading files from the hard drive
- Interacting with a Bluetooth device
- Sending data to a database
Promises help us perform I/O without forcing our entire program to freeze up while we wait for a response.