缺少类型的属性（打字稿）

Question

In the following:

@Mutation
remove_bought_products(productsToBeRemoved: Array<I.Product>) {

    const tmpProductsInVendingMachine: Array<I.Product> = Object.values(this.productsInVendingMachine);
    const reducedProductsInVendingMachine: Array<I.Product> =
        tmpProductsInVendingMachine.reduce((tmpProductsInVendingMachine, { id, ...rest }) => ({ ...tmpProductsInVendingMachine, ...{ [id]: { id, ...rest } } }), {});
    productsToBeRemoved.forEach(({ id }) => reducedProductsInVendingMachine[id].productQty--);
...

gives:

TS2740: Type '{}' is missing the following properties from type 'Product[]': length, pop, 
push, concat, and 28 more.
250 |
251 |         const tmpProductsInVendingMachine: Array<I.Product> = Object.values(this.productsInVendingMachine);
> 252 |         const reducedProductsInVendingMachine: Array<I.Product> =
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
253 |             tmpProductsInVendingMachine.reduce((tmpProductsInVendingMachine, { id, ...rest }) => ({ ...tmpProductsInVendingMachine, ...{ [id]: { id, ...rest } } }), {});
254 |         productsToBeRemoved.forEach(({ id }) => reducedProductsInVendingMachine[id].productQty--);

What type does the reducer return?

Products are objects that need to be indexed over their id; eg

[{
    id: 1,
    productName: "coke",
    productPrice: 2, 
    productQty: 20
},
...
]

Answer 1

reducedProductsInVendingMachine is not an Array , its an Object .

One possibility is to cast {} to the correct type in the initialization parameter of Array.prototype.reduce() :

const reducedProductsInVendingMachine =
    tmpProductsInVendingMachine.reduce(
        (tmpProductsInVendingMachine, { id, ...rest }) =>
            ({ ...tmpProductsInVendingMachine, ...{ [id]: { id, ...rest } } }),
        {} as { [key: I.Product['id']]: I.Product }
    );

Notice how the implementation compiles and the reducedProductsInVendingMachine variable type is correctly inferred to { [key: I.Product['id']]: I.Product } (with I.Product['id'] resolved to whatever it is)