How to find the function name of namespaced constructors in javascript?

Question

For example, compare these two:

function Person(name) {
 this.name = name;
}
var john = new Person('John');
console.log(john.constructor);
// outputs: Person(name)

var MyJSLib = {
 Person : function (name) {
   this.name = name;
 }
}
var john2 = new MyJSLib.Person('John');
console.log(john2.constructor);
// outputs: function()

The first form is useful for debugging at runtime. The 2nd form requires some extra steps to figure out what kind of object you have.

I know that I could write a descriptive toString function or call the toSource method on the constructor to get some more information, but I want the simplest way possible.

Is there a way to do this? Suggestions?

Answer 1

what you want is the name of the holder in the namespace so.

function getName(namespace, obj) {
  for name in namespace:
    if (namespace[name] == obj) return name;
}
console.log(getNameOf(MyJSLib, john2.constructor));

Answer 2

If you want to check whether an object is instance of a specific class then simply use "instanceof" keyword to check that. If you explicitly want a name for the constructor(which I really cannot see a point) you may try the code below

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

Answer 3

Well that happens because you are using an anonymous function.

You can specify names of anonymous functions (yes, it sounds odd), you could:

var MyJSLib = {
 Person : function Person (name) {
   this.name = name;
 }
}
var john2 = new MyJSLib.Person('John');
console.log(john2.constructor);

Anonymous functions can be named but those names are only visible within the functions themselves, and since you use the new operator, the constructor property will be set, and you will be able to see the name.

You could also compare the constructor reference using or not a name for the function:

console.log(john2.constructor === MyJSLib.Person); // true