打字稿：如何定义对象属性的类型？

Question

I have this object in my component

one of its Property has type

interface IProduct {
  artikelname: string
  artikelnummer: string
  barccode: string
}

  form = {
    date: [],
    R2Os: [],
    type: 1,
    cats: null,
    selected_product: Array<IProduct>
  }

but I think this way of typing is not true

and i have error ,

so, how Can I define type for Object Property ?

Answer 1

Normally, you do it by defining a type (like your IProduct ) for the object as a whole, and assigning that type to the variable referring to the object ( form ) when you declare it. For instance:

interface FormType {
    date: Array<something>;
    R20s: Array<something>;
    type: number;
    cats: null | something;
    selected_product: Array<IProduct>;
}
// ...
const form: FormType = {
//        ^^^^^^^^^^−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− giving type to object
    date: [],
    R2Os: [],
    type: 1,
    cats: null,
    selected_product: [],
    //                ^^−−−−−−−−−−−−−−−−−−−−−−−−− value
};

but you can also do it with an inline type assertion:

const form = {
    date: [],
    R2Os: [],
    type: 1,
    cats: null,
    //                vv−−−−−−−−−−−−−−−−−−−−−−−−− value
    selected_product: [] as Array<IProduct>,
    //                  ^^^^^^^^^^^^^^^^^^^−−−−−− type assertion
};

The TypeScript handbook is worth reading from beginning to end. It covers all of the basics in a very concise way.