function array_merge () {
  // http://kevin.vanzonneveld.net
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // +   bugfixed by: Nate
  // +   input by: josh
  // +   bugfixed by: Brett Zamir (http://brett-zamir.me)
  // *     example 1: arr1 = {"color": "red", 0: 2, 1: 4}
  // *     example 1: arr2 = {0: "a", 1: "b", "color": "green", "shape": "trapezoid", 2: 4}
  // *     example 1: array_merge(arr1, arr2)
  // *     returns 1: {"color": "green", 0: 2, 1: 4, 2: "a", 3: "b", "shape": "trapezoid", 4: 4}
  // *     example 2: arr1 = []
  // *     example 2: arr2 = {1: "data"}
  // *     example 2: array_merge(arr1, arr2)
  // *     returns 2: {0: "data"}
  var args = Array.prototype.slice.call(arguments),
    argl = args.length,
    arg,
    retObj = {},
    k = '',
    argil = 0,
    j = 0,
    i = 0,
    ct = 0,
    toStr = Object.prototype.toString,
    retArr = true;

  for (i = 0; i < argl; i++) {
    if (toStr.call(args[i]) !== '[object Array]') {
      retArr = false;
      break;
    }
  }

  if (retArr) {
    retArr = [];
    for (i = 0; i < argl; i++) {
      retArr = retArr.concat(args[i]);
    }
    return retArr;
  }

  for (i = 0, ct = 0; i < argl; i++) {
    arg = args[i];
    if (toStr.call(arg) === '[object Array]') {
      for (j = 0, argil = arg.length; j < argil; j++) {
        retObj[ct++] = arg[j];
      }
    }
    else {
      for (k in arg) {
        if (arg.hasOwnProperty(k)) {
          if (parseInt(k, 10) + '' === k) {
            retObj[ct++] = arg[k];
          }
          else {
            retObj[k] = arg[k];
          }
        }
      }
    }
  }
  return retObj;
}

arr1 = {"color": "red", 0: 2, 1: 4}
arr2 = {0: "a", 1: "b", "color": "green", "shape": "trapezoid", 2: 4}
array_merge(arr1, arr2)

{"color": "green", 0: 2, 1: 4, 2: "a", 3: "b", "shape": "trapezoid", 4: 4}

arr1 = []
arr2 = {1: "data"}
array_merge(arr1, arr2)

{0: "data"}