Why don't people use Object.defineProperty for polyfills?

Question

For example the Mozilla Developer Network simply uses Array.prototype = function to define polyfills, but this creates an enumerable property that breaks for-in loops.

So I used Object.defineProperty(Array.prototype, { enumerable: false ...

Is there some danger to this? Why is this not the common way?

Here is an example polyfill from MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter#Polyfill

Here is the same example with defineProperty:

Object.defineProperty(Array.prototype, {
    enumerable: false,
    value: function(func, thisArg) {
        'use strict';
        if ( ! ((typeof func === 'Function') && this) )
            throw new TypeError();

        var len = this.length >>> 0,
            res = new Array(len), // preallocate array
            c = 0, i = -1;
        if (thisArg === undefined)
          while (++i !== len)
            // checks to see if the key was set
            if (i in this)
              if (func(t[i], i, t))
                res[c++] = t[i];
        else
          while (++i !== len)
            // checks to see if the key was set
            if (i in this)
              if (func.call(thisArg, t[i], i, t))
                res[c++] = t[i];

        res.length = c; // shrink down array to proper size
        return res;
    }
});

Answer 1

Mostly because those polyfills are for ES5 functions, and target an ES3 environment that did not have Object.defineProperty.