I think I have found why I can't use this code:

@JS('L')
library L;

import 'package:js/js.dart';

@JS()
external map(String id);

It's because dart2js creates some global variable L:

// The global objects start as so-called "slow objects". For V8, this
// means that it won't try to make map transitions as we add properties
// to these objects. Later on, we attempt to turn these objects into
// fast objects by calling "convertToFastObject" (see
// [emitConvertToFastObjectFunction]).
...
var K = map();
var L = map();
var M = map();
...

so when my generated code tries to call L.map() it fails because L is empty.

You are correct. For now use somewhat long names for the imported JS libraries to avoid collisions with minified dart2js names. In the future we'll give Dart2JS a list of names to avoid minifying to so this isn't an issue.

@jacob314 I have added window.Leaflet = L; to JS code and changed JS('L') to JS('Leaflet') (my leaflet dart api). Now everything is working good in Chrome, but it still fails in Dartium:

Uncaught Unhandled exception:
TypeError: undefined is not a function
#0      JsFunction._apply (dart:js:1178)
#1      JsFunction.apply (dart:js:1176)
#2      map (package:nova_poshta_osm_sync/leaflet/leaflet.dart_js_interop_patch.dart:19:81)
#3      main.<main_async_body> (http://localhost:8080/app.dart:167:9)
#4      _RootZone.runUnary (dart:async/zone.dart:1149)
#5      _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:502)
#6      _Future._propagateToListeners (dart:async/future_impl.dart:585)
#7      _Future._completeWithValue (dart:async/future_impl.dart:376)
#8      _Future._asyncComplete.<anonymous closure> (dart:async/future_impl.dart:430)
#9      _microtaskLoop (dart:async/schedule_microtask.dart:43)
#10     _microtaskLoopEntry (dart:async/schedule_microtask.dart:52)
#11     _ScheduleImmediateHelper._handleMutation (dart:html:49298)
#12     MutationObserver._create.<anonymous closure> (dart:html:27545)

it fails on this line:

patch map(p0, [p1=_UNDEFINED_JS_CONST]) => js_library.context['Leaflet']['map'].apply([p0,p1].takeWhile((i) => i != _UNDEFINED_JS_CONST).toList());

When I try to repro I get blocked running pub get. Is the pubspec not
configured correctly or do I need to create a separate leaflet pub package
in a sibling directory?

Resolving dependencies...
Could not find package leaflet at "../leaflet.dart".
Depended on by:

• nova_poshta_osm_sync"

On Mon, Dec 28, 2015 at 11:24 AM, Paul Annekov notifications@github.com
wrote:

@jacob314 https://github.com/jacob314 I have added window.Leaflet = L;
to JS code and changed JS('L') to JS('Leaflet') (my leaflet dart api
https://github.com/PaulAnnekov/nova_poshta_osm_sync/blob/master/lib/leaflet/leaflet.dart).
Now everything is working good in Chrome, but it still fails in Dartium:

Uncaught Unhandled exception:
TypeError: undefined is not a function
#0 JsFunction._apply (dart:js:1178)
#1 JsFunction.apply (dart:js:1176)
#2 map (package:nova_poshta_osm_sync/leaflet/leaflet.dart_js_interop_patch.dart:19:81)
#3 main.<main_async_body> (http://localhost:8080/app.dart:167:9)
#4 _RootZone.runUnary (dart:async/zone.dart:1149)
#5 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:502)
#6 _Future._propagateToListeners (dart:async/future_impl.dart:585)
#7 _Future._completeWithValue (dart:async/future_impl.dart:376)
#8 _Future._asyncComplete. (dart:async/future_impl.dart:430)
#9 _microtaskLoop (dart:async/schedule_microtask.dart:43)
#10 _microtaskLoopEntry (dart:async/schedule_microtask.dart:52)
#11 _ScheduleImmediateHelper._handleMutation (dart:html:49298)
#12 MutationObserver._create. (dart:html:27545)

it fails on this line:

patch map(p0, [p1=_UNDEFINED_JS_CONST]) => js_library.context['Leaflet']['map'].apply([p0,p1].takeWhile((i) => i != _UNDEFINED_JS_CONST).toList());

—
Reply to this email directly or view it on GitHub
#25318 (comment).

@jacob314 I have updated the code to make it work for you. Just run pub serve web data.

Thanks Paul. Here's a patch that makes the code work in Dartium and Dart2js.
https://codereview.appspot.com/278650043

The issue is the Leaflet library copies
Array.isArray into a local variable and then uses that copy instead of Array.isArray
Dartium then replaces Array.isArray with a polyfill that also accepts Dart List objects to make JS interop work well for Array/List.
Changing the execution order so the Dart application is loaded before Leaflet fixes the issue.
Longer term, I need to tweak the Dartium polyfill for Array so it executes earlier before any Dart code is executed perhaps immediately on page load regardless of whether the page contains Dart scripts.

Thanks for workaround. Will wait for a clean fix. You can rename issue name to something more relevant.

Duplicate of #25059