Use ES5 built-in function Object.keys -- Don't replace it

[GarrettS]

PrototypeJS defines Object.keys without considering if it is already defined. Instead, it should use the built-in standard, where available:

Prototype 1.6.1:
function keys(object) {
var results = [];
for (var property in object)
results.push(property);
return results;
}

ES5 requires Object.keys TypeError to be thrown there. The for-in loop is required to throw in the same case, where the object is not an object, however for web compat, browsers don't do that. Regardless, for Object.keys(9), Chrome throws.

Instead of calling push, it is faster to increment a variable.

  Object.keys = Object.keys || keys;
 
  function keys(object) {
    if(!(object instanceof Object)) {
      throw TypeError("Object.keys called on non-object");
    }
    var results = [], property, i = 0;
// Preset length, where available.
    results.length = object.__count__ || 0; 
    for (property in object)
  // faster than push()
      results[i++] = property;
    return results;
  }

[kangax]

We can't use native Object.keys as it iterates over own properties only, wheres Prototype's version doesn't; using native Object.keys would result in method behaving differently in different implementations, which is hardly a good idea. Besides, there's a constraint on first argument being an object in ES5 Object.keys (otherwise, TypeError is throw, IIRC), and that is another difference between ES5 and Prototype versions.

Ideally, Prototype should switch to ES5 behavior, but only in next major version (where back-compatibility is not a factor). There are also hundreds of other architecture oversights that make this new, back-incompatible version desirable.

[tobie]

Fixed in master branch.