Types for 'Array.prototype.find()' with an array deconstructor

Question

I am trying to destruct an array, but I am getting the following errors:

Type 'undefined' must have a 'Symbol.iterator' method that returns an iterator.

let [alias, config]: [string, DBConfig] | undefined = Object.entries(info).find(...)

This is what the find definition shows, it is the same as what I defined.

(method) Array<[string, DBConfig]>.find(predicate: (
  value: [string, DBConfig], 
  index: number, 
  obj: [string, DBConfig][]) => boolean, thisArg?: any
): [string, DBConfig] | undefined (+1 overload)

If I remove my definition so it looks like this:

let [alias, config] = Object.entries(info).find(...)

I then get the same error. What can I do (without using any) to get this working?

Vivick · Accepted Answer · 2019-03-27 18:28:20Z

1

The whole problem comes down to the fact that you're trying to use destructuring on something that might not be destrcturable (e.g. undefined).

If you are sure let [alias, config] = Object.entries(info).find(...) will never result in undefined in your use cases then you just have to cast it :

let [alias, config] = Object.entries(info).find(/*...*/) as [string | DBConfig];

If it may result in undefined then you will have to accept a nullable DBConfig

let [alias, config] = Object.entries(info).find(/*...*/) || ["", null];

answered Mar 27, 2019 at 18:28

Vivick

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