operator [] method
dynamic operator [](Returns the value associated with property from the proxied JavaScript object.
The type of property must be either String or num.
Source
operator [](property) {
  try {
    return _operator_getterLegacy(property);
  } catch (e) {
    // Re-throw any errors (returned as a string) as a DomException.
    throw new html.DomException.jsInterop(e);
  }
}
    © 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
    https://api.dartlang.org/stable/1.24.3/dart-js/JsObject/operator_get.html