FormData methods should take a Generic

Suggestion

🔍 Search Terms

Form Data, .entries()

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

FormData entries() method, and perhaps .keys() and .values() should take a generic.

Right now it returns FormDataEntry value and is difficult type type the returned value of that Iterable.

📃 Motivating Example

Example of the problem here:

https://www.typescriptlang.org/play?strictNullChecks=false&target=6#code/PTAEEEGdIVwWwKagIagGYHsBOdQBsBLAayQBcALAyUAgO1AqQBEB5AWQBpQAjGU0AO4EK+ZNwR5qCUgGMAdHIBQMjLUj9MOUAF5QwAFShypOHlD6wAAwA8muAD5FoUNboAHPgwCebhNoBE6lh0AOb+oLTIiAFoBFjq4QQAJjFxCaAAbsh4MH7+AgiQ-o7OrrQe-KQ+eUGh4ZHR-njI6ckBzelZOXncGEWO1sB29pYA3IqKIKAAKuQI9HSgcF4zAMoAXBN0pAhYaMgySAAKu5CqoADeTuhppOugtbQh484ddw+kwU-jAL4TaDBaDJSARzpBkF4ABIEAAUvniqnuJwRtAAlJdrlhpDAsPRLJCECsACQXeFnWhyWLxUg-MaKP7KVTqdDYOAAUTMuiSGBk8HmpDkAEdclgvKsJAhgdgYQByOwy1HjFRqDSspjIUioXS0BACUAAMTVGuQMLsHMVkzAAGFVBldpVyBqHjAZCQsAwMCgFjssGI8AhGSrQEljQBJH1+pC6OzqzVyfnBQowi1TG20O1YB1O4S7SMer2gDDcABWkoFlpmc1AbiwRf9uBUiGocyxXHIGD13NAoaWyBIgkKKFAyPJ3l8AH5QIHmQVqLoWCWy5Ta+zaJ8CEmQ5rw7nuP6LeCobDZxaK7MqMGMPNIDL+AJsERp3fCgAmHSgBel4HLjCr9ebsMIz3BB0RaYdTlUcYz0oahuUKLheH4C9hELIgIUncUEDgahYkgcgvDkKdlRnQoAGZ30-Jc0BXNk10TSAYS3ZAd19YDQOoQEiFoDt6DAkdIMUQ9oRhWdSNPCsWEYd1ZgwGAQmMSB7grABGQjzykAAPKI3H9GhqEgAg4B0hAuB7FQYDwJJe1oGBsjwFYZCxDUyCrIsv1IBDPAoOgiBQXpPGaLAQl2QtF2BSAgA

Feeding the .entries() Iterable into Object.fromEntries(), gives us a type of { [k: string]: FormDataEntryValue; }, and has no overlap between the acutal data (Person in my case) that is supposed to come back.

So perhaps something like formData.entries<Person>() or formData.entries<IterableIterator<Person>>()?

I just know it's really hard to convert the result into a type. And the solutions are either as unknown as Person or a Type Guard, which makes me manually type each property.

💻 Use Cases

See above link example

リンクされている TypeScript playground から始め、FormData.entries()、keys()、values() を Object.fromEntries() に渡したときの型を調べます。要求されているジェネリックな動作と現在の FormDataEntryValue の結果を比較し、安全で破壊的変更のない定義が可能か判断します。完了の条件は、unsafe な assertions なしで動機となった例が有用な型を受け取ることです。