How to use await in map?

Question

There is an array of layes:

this.layers = [
      new ThematicLayers(
        this.userRoles,
        this.layersManager,
        this.map
      ),
      new CommonLayers(
        this.userRoles,
        this.layersManager,
        this.map
      ),
    ];

And abstraction:

export abstract class Layer {
  protected layers: Promise<any> = Promise.resolve(null);

  protected layerGroup: LayerGroup;

  protected grouppedNodes: Map<ITreeNode, ITreeNode[]>;

  abstract load(): Promise<LayerGroup>;

  abstract prepareLayers<T>(layers: T[]): T;

  abstract hasPermission(): boolean;

  abstract createLayersGroup(): void;
 
  get group() {
    return this.layerGroup;
  }

  get stateLayers() {
    return this.reonMap.state;
  }

}

I try iterate the this.layers:

  async getLayersGroups(): Promise<LayerGroup[]> {
    return this.layers.map((layer: Layer) => {
      layer.prepareLayers(await layer.load());
      layer.createLayersGroup();
      return layer.group;
    });
  }

Problem is on line:

layer.prepareLayers(await layer.load());

How to use await in map?

It wouldn't replace `map`. See https://stackoverflow.com/questions/37576685/using-async-await-with-a-foreach-loop — evolutionxbox, Jan 29 '21 at 15:41
Does this answer your question? [Using async/await with a forEach loop](https://stackoverflow.com/questions/37576685/using-async-await-with-a-foreach-loop) — evolutionxbox, Jan 29 '21 at 15:41
Nope, I can not use promise.all because I need to get result not from aboth promises, it can be one. — , Jan 29 '21 at 15:52

Mvrocha · Accepted Answer · 2021-01-29T15:42:09.077

1

The right way would be to add a async in front of the map callback:

 async getLayersGroups(): Promise<LayerGroup[]> {
    return this.layers.map(async(layer: Layer) => {
      layer.prepareLayers(await layer.load());
      layer.createLayersGroup();
      return layer.group;
    });
  }

edited Jan 29 '21 at 15:42

answered Jan 29 '21 at 15:38

Mvrocha

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14

Why did you copy the code and posted them? What is difference? – Jan 29 '21 at 15:39
The difference is the async in fornt of layer: this.layers.map(async(layer: Layer) – Mvrocha Jan 29 '21 at 15:41
Yes, I see sorry, will try – Jan 29 '21 at 15:41
Doesn't `getLayersGroups` still need to be called with `Promise.all`? – evolutionxbox Jan 29 '21 at 15:53
Yes, still be necessary. – Mvrocha Jan 29 '21 at 16:12

How to use await in map?

1 Answers1