获取未定义的地图错误....使用地图时出现打字错误

Question

I'm getting this "TypeError: Cannot read properties of undefined (reading 'map')"

const Categories = () => {
    return (
    <Container>
       {categories.map((item) =>(
        <CategoryItem key={item.id}/>
       ))}
    </Container>
  )
}

Answer 1

categories is undefined so the map function is not available.

if you want to return no category items in this case you can do chained operator to test categories is not null first https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html

 const Categories = () => { return ( <Container> {categories?.map((item) =>( <CategoryItem key={item.id}/> ))} </Container> ) }

Answer 2

这意味着您的categories变量未定义，请确保它确实有一个值并且它是一个有效的数组。