identify ES5 functions that are not implemented in a browser (returns an object literal of arrays that contain the names of the missing functions)

es5check.js

var issues = (function() {
  var o = {
    "Array.prototype": "forEach map reduce reduceRight filter every some indexOf lastIndexOf",
    "Array": "isArray",
    "Object": "keys preventExtensions isExtensible getOwnPropertyDescriptor defineProperty getOwnPropertyNames create seal isSealed freeze isFrozen"
  };

  for(var l in o) {
    o[l] = o[l].split(" ");
    for(var f=0; f<o[l].length; f++) {
      var k = l.split(".");

      if(!!(k[1] ? window[k[0]][k[1]] : window[k[0]])[o[l][f]]) {
        o[l].splice(f, 1); --f;
      }
    }
  }

  return o;
})();

this is not tested with IE. Not sure exactly how dependable it is, i needed it for a pretty narrow edge case. please feel free to mod!!