filter noUncheckedIndexedAccess with own property check #41848
Description
Search Terms
ownProperty
hasOwnProperty
noUncheckedIndexedAccess
type check
Suggestion
noUncheckedIndexedAccess is a great feature. However, ts reports that object can be undefined even with hasOwnProperty check.
I suggest that a hasOwnProperty check makes unchecked indexed accesses checked, and return the checked value.
Use Cases
const obj: {[key: string]: string} = {};
// do something with obj
const key = "someKey";
if (Object.prototype.hasOwnProperty.call(obj, key)) {
console.log(obj[key].length); // TS2532: Object is possibly 'undefined'.
}Since only string values are allowed in obj, the only case such value is undefined is when the key does not exist on obj. The value of obj[key] can only be string. However, typescript still reports type of obj[key] being string | undefined.
Examples
const obj: {[key: string]: string} = {};
// do something with obj
const key = "someKey";
if (Object.prototype.hasOwnProperty.call(obj, key)) {
console.log(obj[key].length); // no problem, since obj[key] has correct type string
}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.
