Small TS strict improvements in trackHistory and batching

[Manc]

In trackHistory an object type was defined as Record<number, Partial<T>>. The keys are timestamps.

However, a test failed (in strict mode) due to a typing error when the key was expected to be a number, but Object.keys() actually returns strings. Object keys are implicitly cast to stings even when set as numbers, so the keys will always be strings.

Unrelated but tiny change: I also added a type for let timeout.

[jmeistrich]

I would prefer to keep the timestamps as numbers because they are smaller in size - a 13 digit timestamp is 8 bytes as a number vs. 26 bytes as a string. It's especially important when persisting the timestamps to a database. Can we improve the types while keeping it as a number?

[Manc]

The problem here is that number keys on a JS object do not exist. If you set a property with a number key, JS will automatically set it with a string key. See here. This is why Object.keys() always returns an Array<string>. So we may as well set the TS key type to string. See also here.

const obj = { 123: true };
obj // { '123': true }

[jmeistrich]

Huh, 10 years into JS development and I never knew that 😅

[Manc]

I know I know, I still find myself learning by simply using TS. I didn’t even look what this history is used for, but if you expect a lot of entries, maybe a tuple array may be more suitable here, like Array<[number, Entry]>.