How to list properties of built-in functions in JavaScript?

Question

When I define an object I can reach all its properties by using the dot character and the same applies to built-in functions like String, Array, Math, etc. But I cannot loop through them by using for(# in # for example. It says String is native code but still I can reach all its members albeit I cannot iterate through them. I know window is iterable but their 'sub-functions' appear to be not. Why is that? Is there a chance to call the properties without explicitly typing their names in? Can I list all its members somehow?

I am aware of that It does not look useful and no one would need it in production. I am asking it because I could not do it and I hope someone can give me some help.

How would you call a member function without knowing its name ? That's king of stupid. If you want to call a function when you only have a String (representing the function's name), juste do object[str](); — Larta
– Larta, Commented Aug 7, 2014 at 9:40

user3917789 · Accepted Answer · 2014-08-07 10:05:00Z

1

You can get all names only of own(!!!) properties

Object.getOwnPropertyNames(YOUR_OBJECT)

It means, this method doesn't enumerate inherited properties. And if you want to enumerate inherited properties you can use YOUR_OBJECT.__proto__, but it works only in Mozilla

answered Aug 7, 2014 at 10:05

user3917789

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6 Comments

Bálint Juhász Over a year ago

@Bergi How would you get a list of the prototypes with this method?

Bergi Over a year ago

for (var prototypes=[], p=YOUR_OBJECt; p=Object.getPrototypeOf(p); prototypes.push(p)); should do it. No difference in functionality to getting __proto__, except for being standard.

user3917789 Over a year ago

@Bergi but you have to stop youe loop when p will equal Object, because Object.getPrototypeOf(Object) == function() {} and you have infinite loop

Bergi Over a year ago

No, you've got something wrong there. Object -> Function.prototype -> Object.prototype -> null. Prototype chains are guaranteed to have no circles, so this cannot be an infinite loop.

user3917789 Over a year ago

@Bálint Juhász getPrototypeOf returns only prototypes, and after that you have to call getOwnPropertyNames() for every prototype.

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