When a function has performed an assignment, it may provide a value that other functions would need, for any reason you judge necessary. When a function produces a value an makes it available to other functions, such a function is said to return a value.
Here is a function that returns a value:
function rectangleArea(length, height)
area = length * height * 3.14159;
Even if a function returns a value, it can still be called like any other function. If a function returns a value, its name can be assigned to a variable to give a value to, or change the value of, the variable. Here is an example: