[PERF] fix sub-optimal compiler output

[stefanpenner]

given:

let [a, b] = thing;

If it is not statically known to babel, it will assume an iterator may be present. At which the following code is omitted.

var _changedAttributes$attribute = _slicedToArray(changedAttributes[attribute], 2);

var oldData = _changedAttributes$attribute[0];
var newData = _changedAttributes$attribute[1];

  var _slicedToArray = (function () {
    function sliceIterator(arr, i) {
      var _arr = [];var _n = true;var _d = false;var _e = undefined;try {
        for (var _i = arr[Symbol.iterator](), _s; !(_n = (_s = _i.next()).done); _n = true) {
          _arr.push(_s.value);if (i && _arr.length === i) break;
        }
      } catch (err) {
        _d = true;_e = err;
      } finally {
        try {
          if (!_n && _i["return"]) _i["return"]();
        } finally {
          if (_d) throw _e;
        }
      }return _arr;
    }return function (arr, i) {
      if (Array.isArray(arr)) {
        return arr;
      } else if (Symbol.iterator in Object(arr)) {
        return sliceIterator(arr, i);
      } else {
        throw new TypeError("Invalid attempt to destructure non-iterable instance");
      }
    };
  })();

instead of the expected:

let a = thing[0];
let b = thing[1];

[bmac]

let newData = data[1];

[rwjblue]

@stefanpenner - Are we sure we are using loose mode? I tested this method via Babel 5 REPL and it does the simple thing you have done:

Babel 5 REPL Demo

[rwjblue]

I do see that in our bower builds we are including the _slicedToArray helper as you mentioned (see here).