How to get all the properties assigned to the function object in javascript?

Question

In javascript I can create an object with the same name as a function, or i can assign a new property to the function object, like:

 function func(){ console.log("inside func"); } func.a = "new property"; console.log(func.a); func(); console.log(func);

How do i see what are the properties assigned(and possibly their values) to the function object?

Answer 1

Functions are special type of Objects in JavaScript.

Unlike other programming languages, functions are special type of Objects in JavaScript. They have their own methods (viz. bind, call, apply and a hell lot more) like other objects do. Therefore, when you assign a prop a to your func , you are not creating a new func object. Instead, it's the same func object (function object) and you are just creating a new prop func.a on it. Read this for more info. Also, you can do something like the following to print all the props you have assigned to a function object (or any object in JS):

for (var prop in func) {
  console.log(prop); // This will print 'a' in your case
}

Answer 2

最直接的方法可能是这样的：

Object.getOwnPropertyNames(func);

Answer 3

The function is implicitely cast to string when console.log() is called, and by default toString() only returns the code of your function (see the documentation here ).

function func(){
  console.log("inside func");
}
func.toString = function() {
  return "a = " + this.a;
}
func.a = "new attribute";
console.log(func.a);
func();
console.log(func);