Description
Suggestion
Like with ways for adding and removing optionality form properties ?/- there seams to be a need to remove the special undefinedness of properties introduced in noUncheckedIndexedAccess:true
🔍 Search Terms
noUncheckedIndexedAccess Record Array
✅ 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.
📃 Motivating Example
With noUncheckedIndexedAccess:false we have a notion of Record that defines values, for all the possible properties. In practice there are not many actual values like that. Point ofnoUncheckedIndexedAccess:true was to automatically add | undefined type to result of property access so we are more type-safe automatically.
The main TypeSafe use-case for the records which do have value for any possible key are Proxies. And looks like we have lost a way to express the those properly with noUncheckedIndexedAccess:true
💻 Use Cases
Imagine
const val = new Proxy<{[k in string]: string}>({}, {
get: (_, p) => p.toString().toUpperCase()
});
const foo = val.foowith noUncheckedIndexedAccess:false, typer of foo is string tho with noUncheckedIndexedAccess:true, foo has type: string | undefined which is not correct. here we know 100% that any value we read from val via property access, must be string, but it can't be expressed using Typescript when noUncheckedIndexedAccess:true.
We can visualize what we lost using this table:
| noUncheckedIndexedAccess:false | Record<string,string> | Record<string,string | undefiend> |
| noUncheckedIndexedAccess:true | _____________________ | Record<string,string> |