CODEWITHSUNDEEP
javascriptarraystypescriptsortingundefined
tothemoon
tothemoon

Reputation: 11

How to resolve Typescript "Object is possibly undefined" warning when sorting objects by property value in Javascript

I have an array of objects that I'm sorting by the value of one of the properties. The sort is working correctly but I'm getting a Typescript warning that "Object is possibly 'undefined'"

How do I check for undefined values on name to resolve this warning?

myItems.sort((a, b) => (a.name > b.name  ? 1 : -1));

Upvotes: 1

Views: 5799

Answers (1)

Alex Wayne
Alex Wayne

Reputation: 187034

Typescript is telling you there is a bug in your code. The type of your array apparently is something like:

({ name: string } | undefined)[]

That means that when you iterate over that array, you need to handle the case where the item is undefined, otherwise (undefined).name will throw a runtime error.

The easiest way to fix this is probably to filter your array so it no longer includes any undefined values:

interface MyItem { name: string }

const myItems: (MyItem | undefined)[] = [
  { name: 'c' },
  { name: 'b' },
  undefined,
  { name: 'a' },
]

myItems
  .filter((item): item is MyItem => !!item)
  .sort((a, b) => (a.name > b.name  ? 1 : -1));

This uses a filter function that is also a typeguard. After it runs, the returned array will be of type MyItem[], and then your sort can run correctly knowing that all items have a value.

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Upvotes: 4

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