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)
2 options come to my mind:
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.
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)
})
num is undefined. I'd really recommend against the particular choice here, though, since it's not a consistent comparison function. Among other things, comparison functions should be transitive, but your function will have {a: 1} compare as equal to both {a: 2, num: 2} and {a: 3, num: 3}, which will not compare equal to each other. This will yield "implementation defined" sorting results, which is unlikely to be what anyone wants. Maybe (a.num ?? -Infinity) - (b.num ?? Infinity) instead? 🤷♂️
filter.a is relevant to the order, so it should be used instead.To add to AqueleHugo's answer, I wanted to keep the field optional (to correctly reflect the 3rd party's interface), but still keep it clean, simple and readable, so I've gone with this and it works well for my situation:
interface WebPage {
// ...
order?: number;
}
const sortPages = (pages: WebPage[]): WebPage[] => {
return pages.filter(p => p.order).sort((p1, p2) => Number(p1.order) - Number(p2.order));
}
Hopefully someone else finds this useful!
[ {a:1}, {a:2}, {a:3, num: 10}]const filter: Filter[]instead ofconst filter: Filter?numshould be placed before those have a defined value."