Returning Functions

Because functions are values, functions can return other functions. This can be incredibly powerful.

var makeFunction = function () { var addOne = function (x) { return x + 1; }; return addOne; // return the function }; // makeFunction is a function with no arguments var f = makeFunction(); // f is a function that takes one argument var y = f(3); // now y is 4

Remember there's a difference between a function and a function applied to its arguments. It's the difference between f and f(x). If a function doesn't take any arguments there is still a difference. makeFunction is a function that takes no arguments, makeFunction() is the result of calling that function. Which is itself another function...

Define a function named generate that takes one argument, a function f. It should return an array that consists of the function f and another function that doubles its input.