Eloquent JavaScript, 2nd Edition, Chapter 5 Higher-Order Functions

Question

I\'m very new to JavaScript, and I was hoping to get some help with Chapter 5 in the 2nd Ed. of Eloquent JavaScript. Specifically, I ran into the example below:

Answer 1

noisy is a function that takes a reference to another function f and returns a new function that wraps f so that it's call and return values are logged to the console.

val is the result of the function f being called, where f is a function reference that is passed when noisy is called.

To go step by step:

// noisy accepts argument f (where f itself appears to be a function)
function noisy(f) {
    // noisy returns a new function that takes an argument arg
    return function(arg) {
        // when this new function is called, it logs to console
        console.log("calling with", arg);
        // the function you originally passed to noisy is now called, with the return value stored in val
        var val = f(arg);
        // return value val also logged to console
        console.log("called with", arg, "- got", val);
        // return value val is returned from the generated function
        return val;
    };
}
// noisy is called with the inbuilt function Boolean and the argument 0 (to test the boolean value of 0)
noisy(Boolean)(0);

Another use case could be something like this:

function someFuncToMonitor(someArg) {
    return someArg + 1;
}
monitoredFunc = noisy(someFuncToMonitor);
result = monitoredFunc(5);
// calling with 5
// calling with 5 - got 6

So in short calling monitoredFunc calls your someFuncToMonitor function for you and tells you about the call and the results.