javascript中函数和对象的本质区别是什么？

Question

When I learn js at first I get a voice which say everything is an object, so I think maybe function is an object and object is an object too.

But when I learn prototype, some thing different to my thought.

function helloworld(){                                                                       
    this.hi = 'world';
}
var foo = { 
    'sth':'happend'
};


function bar(){};

bar.prototype = foo;
console.log(new bar().sth);

bar.prototype = helloworld;
console.log(new bar().hi);

And I get print

happend
undefined

Then I replace bar.prototype = helloworld; to bar.prototype = new helloworld(); I get correct result.

happend
world

I'm a newbie, maybe it's a stupid question, but I really want to know what's wrong in my mind? is function not an Object? could anybody help me? thanks a lot..

Answer 1

Yes, a function is an object, and can have properties as well:

var foo = {};
var bar = function(x){return x+1};
foo.prop = "hello ";
bar.prop = "world!"; // works the same!
alert(foo.prop + bar.prop);

What's substantive difference between function and Object?

Well, a function is an object that can be called - "normal" objects can't:

bar(4); // 5
foo(4); // Error: 'foo' is not a function

I replace bar.prototype = helloworld; with bar.prototype = new helloworld(); to get correct result

I really want to know what's wrong in my mind?

You must not confuse constructor functions for instances that were created by calling them. helloworld is an object (just as bar is in the example above), but it's a very different object than new helloworld() (which inherits from helloworld.prototype , and was initialised by the constructor with a hi property).