How can a javascript function also be an object?

Question

This is a tough one to word, but how can you have Model.method() and Model() be valid at the same time? The particular library that makes me ask this is mongoose (http://mongoosejs.com/docs/) where Model as an object represents a mongo collection and has several methods and Model as a function is a constructor for a mongo document with some methods. I'm trying to do something similar, but it just returns a function making typeof Model === 'function' and never object. It is as follows:

let model = (function(){
        for(var i in queries){
            if(typeof i == 'function'){
                if(i == 'insert'){
                    continue;
                }
                this[i] = function(){
                    queries[i].apply(this, arguments); // queries is a separate module I've written that has methods for querying a DB
                };
            }
        }
        return (function(){
            for(var i in arguments[0]){
                if(!(i in schema) && typeof arguments[0][i] != typeof schema[i]){
                    this[i] = arguments[0][i];
                }
                else{
                    throw new Error('Invalid argument, key: ' + i + ' value: ' + arguments[0][i]);
                }
            }
            for(var i in schema.methods){
                this[i] = schema.methods[i];
            }
        });
    })();

"How can a javascript object also be a function?" It's more the other way around, JavaScript functions are objects (always). — T.J. Crowder
– T.J. Crowder, Commented Sep 30, 2015 at 14:34
That said, I don't see any particular properties being put on the function that ends up assigned to model. The fact it's an object isn't really being used (other than that we can have a reference to it) in the quoted code. — T.J. Crowder
– T.J. Crowder, Commented Sep 30, 2015 at 14:36

Quentin · Accepted Answer · 2015-09-30 14:29:35Z

5

All JavaScript functions are objects. That's just how JavaScript works.

function alert(message) {
    document.body.appendChild(document.createTextNode(message));
    document.body.appendChild(document.createElement('br'));
}

function myFunction() {
  alert("This is myFunction");
}

myFunction.property = "Hello";

myFunction.recursive = myFunction;

myFunction();
alert(myFunction.property);
alert(myFunction.name);
myFunction.recursive.recursive.recursive.recursive.recursive();

answered Sep 30, 2015 at 14:29

Quentin

948k136 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Michele Locati · Accepted Answer · 2015-09-30 14:31:53Z

0

JavaScript functions are a special kind of JavaScript objects. That means that all the functions are objects, but objects are not necessarily functions.

answered Sep 30, 2015 at 14:31

Michele Locati

1,86422 silver badges26 bronze badges

Collectives™ on Stack Overflow

How can a javascript function also be an object?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related