How to print all functions of JavaScript non-objects?

Question

If I have var foo = 'bar';, how do I get all the functions callable on foo, such as toUpperCase? It's not an object, so Object.getOwnPropertyNames(foo) doesn't work:

$ node
> var foo = 'bar';
undefined
> console.log(Object.getOwnPropertyNames(foo));
TypeError: Object.getOwnPropertyNames called on non-object
    at Function.getOwnPropertyNames (native)
    at repl:1:20
    at REPLServer.eval (repl.js:80:21)
    at repl.js:190:20
    at REPLServer.eval (repl.js:87:5)
    at Interface.<anonymous> (repl.js:182:12)
    at Interface.emit (events.js:67:17)
    at Interface._onLine (readline.js:162:10)
    at Interface._line (readline.js:426:8)
    at Interface._ttyWrite (readline.js:603:14)

katspaugh's simple, elegant solution:

> console.log(Object.getOwnPropertyNames(foo.constructor.prototype));
[ 'constructor',
  'length',
  'toLowerCase',
  ... ]
undefined

I'm pretty sure it is an object. Though the properties you are looking for might not be its "own". Have you tried something like Object.keys(foo)? — J. Holmes
– J. Holmes, Commented Apr 25, 2012 at 8:46
@32bitkid - It's not an object, it's a primitive string value. It will sometimes be temporarily cast to an instance of String (if you call a method of String.prototype on it for example). l0b0 - Do you want this for a general case (any type) or just for strings? — James Allardice
– James Allardice, Commented Apr 25, 2012 at 8:48
@32bitkid - As far as I know, it's just a string literal until you use it as object [ref]. I guess this question is all about getting properties from String, which is exactly what the linked question talks about. — Álvaro González
– Álvaro González, Commented Apr 25, 2012 at 8:50
@James_Allardice right on, sometimes my brain goes a little loopy at 4am. Insomnia wins again — J. Holmes
– J. Holmes, Commented Apr 25, 2012 at 8:51
I'm not sure you can do it. Although, if you enter "String.prototype" in Chrome's console. You get all the methods. — Lee Kowalkowski
– Lee Kowalkowski, Commented Apr 25, 2012 at 9:00

katspaugh · Accepted Answer · 2012-04-25 09:01:10Z

3

The methods you want are on the String.prototype, the prototype of all strings, ruler of Valindor.

Object.getOwnPropertyNames('baz'.constructor.prototype)

answered Apr 25, 2012 at 9:01

katspaugh

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3 Comments

James Allardice Over a year ago

+1, I knew there was a way! This will work for all primitive values too.

Leonid Over a year ago

Could be Object.getOwnPropertyNames(Object(whatever)) as well.

katspaugh Over a year ago

@SomeGuy, you mean Object.getOwnPropertyNames(Object.getPrototypeOf(Object(whatever))).

HGK · Accepted Answer · 2012-04-25 09:14:47Z

1

use can use the below:

$(document).ready(function () {
    var foo = 'bar';
    var div = '';
    var ob = Object.getOwnPropertyNames(foo.constructor.prototype);
    for (var i = 0; i < ob.length; i++) {
        div += ob[i] + "<br/>";
    }
    $(selector).html(div);
});

edited Apr 25, 2012 at 9:14

answered Apr 25, 2012 at 8:58

HGK

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1 Comment

l0b0 Over a year ago

That's a lot of unnecessary boilerplate code for essentially the same solution as @katspaugh. But it's valid, so +1.

katspaugh · Accepted Answer · 2012-04-25 08:57:14Z

-2

Use eclipse :)

Or just look here: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String

edited Apr 25, 2012 at 8:57

katspaugh

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answered Apr 25, 2012 at 8:43

Pulkit Mittal

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