Creating a Dart List from a Javascript array

dart, javascript

Solution

There's no built-in way in js-interop for now to use Dart `List` when a js `Array` is returned.

`directionsLeg.steps` returns a `js.Proxy` which handles like js `Array`. You can iterate on it like this :

final steps = directionsLeg.steps;
for (var i = 0; i < steps.length ; i++) {
  final step = steps[i];
  // do the job with step
}

If you really want to use a Dart `List` you can convert the `js.Proxy` of js `Array` to a Dart `List` with something like :

List<js.Proxy> convertToList(js.Proxy arrayProxy){
  final result = new List<js.Proxy>();
  for (var i = 0; i < arrayProxy.length ; i++) {
    result.add(arrayProxy[i]);
  }
  return result;
}

About your code :

- You can't define `List<maps.DirectionsStep>` : `maps.DirectionsStep` is not a type, it's a `js.Proxy` on js `google.maps.DirectionsStep` (moreover it don't really exist - only a container js object `{}`).

- `List.from(...)` : here, you try to call a static method named `from` on Dart `List` object. That why you get your error. `List.from` is actually a factory named constructor and has to be used with the `new` keyword ( `new List.from(otherIterable)` ).

Problem

I am trying to learn client-side Dart, coming from a server-side Java EE world, and I am having trouble converting an array from an existing JavaScript library into a Dart List. I am trying to learn by building on the Javascript Interop example that uses Google Maps. In Google's Maps API's documentation, the `DirectionsLeg` object's `step` property returns. array of DirectionsSteps, each of which contains information about the individual steps in this leg How can I convert this `var` into a Dart List? I have tried the following: ``` final List<maps.DirectionsStep> steps = List.from(directionsLeg.steps); ``` But Dart Editor tells me `cannot resolve method 'from' in class 'List'`. My imports are: ``` import 'dart:html'; import 'dart:core'; import 'package:js/js.dart' as js; ``` What am I doing wrong? Is it even possible or must I just accept using a `var`?

Original source