type MaybeThereIsAValue = {
[p: string]: string | undefined
}
...
let bar: MaybeThereIsAValue = {};
const key = "carpe";
bar[key] = "diem";
const why = bar[key];
// why is string | undefined
I am confused as to why why is showing as string | undefined, even though I am clearly assigning a value to bar[key] in the line above?
What could be causing this and how can I resolve it?
https://i.stack.imgur.com/GDBEhm.png
Please refer to the example here
I understand the reasoning behind that.
The reason is because the strictNullChecks setting in tsconfig is set to true by default, even though its default value is false,
Also, the line const key = 'carpe' gets executed only after TypeScript is compiled into JavaScript, causing TypeScript to be unaware of which key it refers to.
strictNullChecks: Considers null and undefined during type checking.
To address this issue, I suggest two solutions:
1. Change the strictNullChecks setting in tsconfig to false
2. Utilize the ! operator from non-null assertion operator
const why = bar[key]!;
Consider this scenario:
let key = 'carpe';
bar[key] = 'diem';
// The following line will only run after TS is compiled into JS.
key = 'test';
// Therefore, TS cannot determine if the key is 'test' or 'carpe'
// Hence, `why` can be of type string or undefined
const why = bar[key];
If you disable strictNullChecks, why will consistently remain a string type.
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