operator []= method

void operator []= (dynamic index, E value)

Sets the value associated with property on the proxied JavaScript object.

The type of property must be either String or num.

Implementation 

void operator []=(index, E value) {
  // TODO(justinfagnani): fix the semantics for non-ints
  // dartbug.com/14605
  if (index is num && index == index.toInt()) {
    _checkIndex(index);
  }
  super[index] = value;
}