Assignment of type 'Angular Promise<void>' is not compatible

In the process of developing a website with Angular4 and retrieving data from Contentful CMS API, I am encountering an issue with assigning proper types to the returned data despite seeing the correct types in the console.

The example mock data is as follows:

export const NAMES: Page[] = content.getEntries({
    content_type: 'mainMenu'
}).then(function(response){
 response.items.forEach(element => {
   return element.fields;  
 })
});

When displayed in the console using console.log, the data appears like this:

Object { title: "About Aliens" }
Object { title: "Portfolio" }
Object { title: "Meet the team" }
Object { title: "Contact us" }

Here is the class I have used to assign these data types:

export class Page {
  title: string;
}

Being new to Typescript, I am seeking guidance on where I may have gone wrong. Any assistance on mastering the handling of such data from any API would be greatly appreciated.

Thank you.

Answer №1

  1. It is important to assign a promise to an array within the callback of the promise, rather than directly.
  2. If the then call on the promise does not return anything and you need to create or return something, consider using map instead of forEach.
  3. Using an arrow function for the promise callback allows access to this if needed.
  4. When dealing with types in TypeScript, it's recommended to use interfaces instead of concrete types unless specific behavior needs to be added.

The solution:

export NAMES: IPage[]; // no assignment at this point

Call getEntries from a method like so:

content.getEntries({
    content_type: 'mainMenu'
}).then((response) => {
   NAMES = response.items.map(element => element as IPage);
});

IPage

export interface IPage {
  title: string;
}

Answer №2

Utilize your page class as an interface for type assertion without having to instantiate it, similar to the example below

export interface Page { heading : string }

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