Creating an object in JavaScript using an array type初始化数组类型为对象javascript

In my code, there is an interface defined as Products

 export interface Products{
    category: string;
    imageUrl: string;
    price: number;
    title: string;
 }

Within my component, I have a variable named products which is an array of type Products

products: Products[];

I am currently attempting to map the response from my service to the products variable, but I encounter an error stating Type

'{}[]' is not assignable to type 'Products[]'

The cause of this error is unclear to me at the moment

this.subscription = this.productService
  .getAll()
  .subscribe(
    products =>
      (this.products = products.map(p => ({ ...(p.payload.val() as {}) }))),
  )
javascripttypescriptfirebase-realtime-databaseangular8

Answer №1

When looking at this assignment clause:

this.products = products.map(p => ({
  ...(p.payload.val() as {})
}))

The code is casting p.payload.val() to type {} and then spreading it into an empty object, which effectively clones it while maintaining the type as {}. Consequently, products.map(...) results in a type of {}[], also known as Array<{}>. Given that this.products is a collection of Product[], there exists a type incompatibility.

If p.payload.val() already possesses a type of Product, there is no necessity for any casting:

this.products = products.map(p => p.payload.val())

// or if you require the cloning functionality...

this.products = products.map(p => ({ ...p.payload.val() }))

If p.payload.val() does not have the type Product, the correct move would be to cast it directly to Product instead of {}:

this.products = products.map(p => p.payload.val() as Product)

// alternatively, for cloning purposes...

this.products = products.map(p => {
  return { ...p.payload.val() } as Product
});

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