Referencing functions I haven't defined yet in Node modules

Question

If I'm defining a module with the following code:

module.exports = Person;

function Person (name) {
    this.name = name;
};

How come when I require this file the first line doesn't return a ReferenceError, since I haven't defined Person yet?

Answer 1

The entire JS file is parsed FIRST before anything is executed. Thus, the function Person() exists from the parse step before the line module.exports = Person is actually executed.

So, when you do it your way:

// Person already exists and is a function
module.exports = Person;

function Person (name) {
    this.name = name;
};

everything works fine because the definition of Person() is picked up in the parse stage before execution.

But, if you did it like this:

// Person exists, but has no value yet (will be undefined)
module.exports = Person;

var Person = function(name) {
    this.name = name;
};

It would not work because the Person variable would not yet have been assigned when the module.exports = Person line executes. This is one of the main differences between these two methods of defining a function (the timing of when the function is actually available).