从数组的 object 中排序键的值，该键是 typescript 中的可选类型？

Question

What is the best practice for me to sort an object of array by value of key that key is optional type from Object? I have following code that works if num is not optional type However, I got error that Object is possibly 'undefined'.

type Filter = {
    a: number;
    num?: number

}
const filter: Filter[] = [{a: 1, num: 10}, {a: 1, num: 12}, {a: 1, num: 5}]
filter.sort((a,b)=> (a.num > b.num ? 1 : -1))
console.log(filter)

Answer 1

2 options come to my mind:

1. The obvious one: use a type where num is not optional. You can use the Required utility type if you do not want to keep both types without rewriting the properties.

2. If you cannot change the type, that probably means you really want that property to be optional. So you simply should check for it in your sort function. You need to check if num is undefined and decide what to return when that occurs. When you check it, Typescript will infer everything that falls out of that condition will be defined. For instance:

filter.sort((a,b)=> {
  if (typeof a.num === 'undefined' || typeof b.num === 'undefined') {
    return 0;
  }
  return (a.num > b.num ? 1 : -1)
})