what is the difference between var a = {} and var a = function(){}

Question

I got confused about these two , var a = {} and var a = function(){}
a is an object in the first case , a is a function in the second case. And function is also a object. what is the difference?

• Adriano Repetti: Try to invoke an object and you'll see (or to send to server a function)...
• charlietfl: question is very vague. typeof for each is different. Please provide more context as to why you are asking the difference
• blex: Each has a different constructor: jsfiddle.net/qm52hc1u/1
• Radio: duplicate stackoverflow.com/questions/4125479/…

Answer 1

A function is a type of an object in Javascript, but a empty function (function(){}) is very different from an empty object ({}). The easiest way to see the difference is to just execute them and see what they do differently. Using the console you can play around and see how they are different.

 var emptyFunction = function() {}
 console.log(emptyFunction) // function(){}
 console.log(typeof emptyFunction) //"function"
 var emptyObject = {}
 console.log(emptyObject) //Object{}
 console.log(emptyObject) // "object"
 emptyFunction() // returns undefined because your function has no return
 emptyObject() // Uncaught TypeError: object is not a function

The first thing is the type of them are different things as the typeof operator indicates. It shows you what Javascript thinks of the type The last line is where you really start to see the difference. A function is able to be invoked by using () to call it. An object does not have that ability and it will cause an error because the type Object doesn't have a behavior defined for it that involves using the ()

As you pointed out though, a function is just a specific type of object so it can do the same sort of things an object. So we can do something like this:

emptyFunction.foo = function(){ return 'foo';} console.log(emptyFunction.foo()) //'foo' emptyObject.bar = function(){ return 'bar';} console.log(emptyObject.bar()) //'bar'

As you can see when it comes down to it, the difference is a function is a specialized object that can be invoked. You can read more about functions in Javascript here

• Xuzheng Wang: Thanks for response. Since they are similar. In which situation, var a = {} is better choice and in which situation , var a = function () {} is a better choice?
• Craig Suchanec: Asking that questions shows a lack of understanding of functions and objects in general. You really need to look at the fundamentals of the language. An empty function is completely useless as it just returns undefined and doesn't do anything. You wouldn't use it in any real scenario I can think of. You use a function when you need a sub-routine in your program. A subroutine that returns undefined and does nothings is useless.
• Xuzheng Wang: Sorry I did not make it clear. I meant var a = { code goes here} and var a = function (){ code goes here} . They are not empty. These two things can do the same thing. So, in which situation , one is desirable?