Functions are true values?

Question

I've just started reading JavaScript: The Definitive Guide and I don't understand what the author means when he says:

"The most important thing about functions in JavaScript is that they are true values and that JavaScript programs can treat them like regular objects."

What does he mean that they are "true values"? And why does this mean that they can be treated like objects?

Answer 1

It means JavaScript does not make a distinction between functions or strings, or numbers or booleans, as far as it is concerned they're all the same.

They're all objects.

Objects are key/value pairs in JS, just like

"neilmunro".length;

Will be 9.

function sayHi() { console.log("Hi"); }
sayHi.name;

Will print out "sayHi".

Functions can be passed to other functions:

function doSomething(name, func) {
    console.log("Hi: " + name);
    func();
}

doSomething("Neil", function() { console.log("You're a human!"); });

It's a bit mind bending, and there's a lot more to it than just that, but it's the basic idea.