Higher-order fuctions are functions that take in other functions as parameters, return a function as an output, or both
- In JavaScript, functions are obects
- Functions are first class objects, meaning they have properties and methods like any other objects
- Functions work like any other data types, meaning they can be reassigned to other variables and taken as parameters/arguments in other functions
- When a function is used as an argument to a higher-order function, the function is called a callback function -> the function is not 'called' or 'invoked' to return the output of the function call, but is 'called back' to refer to the function itself by the higher-order function.
> when using callback functions, you write only the function's name without(). The()used with the function name is for function calls.
> this also applies when you assign a function to a new variable -> you are not assigning the result of the function call to the new variable. you are assigning the function itself to the new variable for an easier callback later on
