Is it possible to emulate non-enumerable properties?

Question

ES5 has a enumerable flag. Example

Example

var getOwnPropertyDescriptor = Object.getOwnPropertyDescriptor
 , pd = getOwnPropertyDescriptor(Object.p         


        

Answer 1

If you do care a lot about IE8/IE7 then you can do

for (p in o) {
   if (o.hasOwnProperty(p)) { body } 
}

There is no real "hack" alternative but this could be a work-around for simple cases

The accepted answer doesn't really work for literals i.e. strings "", numbers 3, or booleans true

Answer 2

You can do it via code-rewriting. Rewrite every use of for (p in o) body to

for (p in o) {
  if (!(/^__notenum_/.test(p) || o['__notenum_' + p])) {
    body
  } 
}

and then you can mark properties not enumerable by defining a __notenum_... property. To be compatible you would have to tweak the above to make sure that __notenum_propname is defined at the same prototype level as propname, and if you use them, overwrite eval and new Function to rewrite.

That's basically what ES5/3 does.

Answer 3

Partial.js by Jake Verbaten is the answer to it.

The partial.js is as follows

/* partial non-enumerable property implementation

  Adds a flag to a weakmap saying on obj foo property bar is not enumerable.

  Then checks that flag in Object.keys emulation.
*/

// pd.Name :- https://github.com/Raynos/pd#pd.Name
var enumerables = pd.Name();

Object.defineProperty = function (obj, name, prop) {
    if (prop.enumerable === false) {
         enumerables(obj)[name] = true;
    }
    ...
};

Object.keys = function (obj) {
    var enumerabilityHash = enumerables(obj), keys = [];
    for (var k in obj) {
        if (obj.hasOwnProperty(k) && !enumerabilityHash[k]) {
             keys.push(k);
        }
    }
    return keys;
};

Object.getOwnPropertyNames = function (obj) {
    var keys = [];
    for (var k in obj) { 
        if (obj.hasOwnProperty(k)) {
             keys.push(k);
        }
    }
};

I hope this helps the guys searching for this fix.