another way of noUncheckedIndexedAccess #41711
Description
Search Terms
Suggestion
tsconfig: noUncheckedIndexedAccess is a good new feature, but whole project level setting is too coarse-grained to use.
traditional { [index :number] :undefined | T } could control that in api level. but not like noUncheckedIndexedAccess, it makes arr[0] = undefined valid which is not intended.
I wait the feature so long, but when I open noUncheckedIndexedAccess, there are too many too many too many errors, which cause trouble far more than help.
so in fact, we need a feature that makes T-only when writing, and T | undefined when reading.
Use Cases
Examples
maybe something like:
type T = string;
const myArray :{
optional [index :number] :T
optional item :T
};
myArray[0]// T | undefined
myArray.item// T | undefined
myArray.item = undefined// error, undefined is readonly
if ( 'item' in myArray ) {
myArray.item// T
}
? to be rethinked would be best, but it took too much historical burden.
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, etc.)
- This feature would agree with the rest of TypeScript's Design Goals.