+= in an array

[analog owl]

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAhgJwXAnjAvDA2gRgDQwBMBYArgDbkC6AUDaJLAJZgAmApgB4YwCsdiZCiwsOnKjAA+kzAAYag1CLZcJAakwBmOuXbMVnAEI9+CpEtFdDE6XLNDlY6zA0xNQA

Why does this work with a const, but not a let? Even if the variable was reassigned, it should still work.

[dim path]

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engardiun#0

Playground Link

Preview:```ts
const array = [1, 2, null]

const index = 5

array[index] ||= 0
array[index] += 3

let indexB = 5

array[indexB] ||= 0
array[indexB] += 3```

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[main rover]

In the case of const index = 5, TS knows that it cannot change, and array[index] ||= 0 ensures that element cannot be null, so the latter += 3 is allowed.