类型“ any []”的参数不能分配给类型“ A”的参数。 类型“ any []”中缺少属性“ a”

Question

I'm a very beginner in TypeScript and now I'm trying to understand how interfaces works in a Class Method of React Component. I created a simple case for it, but it does not work. I always gets an error like in this post title.

I'll be pleased for any help.

import React, { Component } from 'react'

interface A {
  a: any[]
}

class Test extends Component {
  _getName = (a: A) => {
    return a
  }
  render() {
    const a = []
    return (
      <div>{this._getName(a)}</div>
    )
  }
}

export default Test

Answer 1

this._getName(a) expects a to be of type A . A is defined as an object with a property a that is of type any[] . Your call-time a inside render is of type [] .

I'm not sure what it is you are trying to accomplish with this code but I guess what you want is to say that the parameter a in _getName should be of type any[] ? Then you probably need type A = any[] .

Answer 2

interface A {
  a: any[]
}

means that the object that implements the interface "A" is required to have a property called "a" that will be of type "any[]" (array of any type)

but here:

const a = []

it looks like a is just an empty array - not an object, thus not having properties

In my opinion you don't need an interface here. Try instead:

  _getName = (a: any[]) => {
    return a
  }

Answer 3

It is necessary to do so:

class Test extends Component {
  _getName = (a: A) => {
    return a.a;
  }
  render() {
    const a = {a: []};
    return this._getName(a);
  }
}