Descending ULID about javascript HOT 8 CLOSED

Hi @frikishaan !
This is my solution:

const enc = '0123456789ABCDEFGHJKMNPQRSTVWXYZ';
function rev(ulid) { return [...ulid].map(x => enc[31 - enc.indexOf(x)]).join(''); }

// Test!
const ulid1 = '01ARZ3NDEKTSV4RRFFQ69G5FAV';
const ulid2 = '01ARYZ6S41TSV4RRFFQ69G5FAV';
console.log(ulid1 > ulid2);  // => true
console.log(rev(ulid1) < rev(ulid2));  // => true

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@frikishaan

have you tested it in production?

No.

is it collision free?

Yes, the probability of collision for "descending ULIDs" is the same as that of the original ULIDs because rev function is bijective.
You can convert a "descending ULID" back to the original ULID by applying the rev function once more.

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Would reversing the lexicographical sort (with positive timestamps) work for you? If not, then I don't exactly understand your problem. Before making changes to handle negative timestamps, I'd like to understand what you're trying to do.

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Reversing the lexicographic sort does solve the problem. I basically needed a way to create "descending" ulids

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What is the problem you are trying to solve by using negative timestamps?

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@thdxr, I'm assuming your problem has been solved, and closing this issue. Feel free to open it up again if things don't work for you!

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@thdxr Were you able to solve the problem? Would you mind sharing the solution here?

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Hi @gkkachi,
Thanks, have you tested it in production, is it collision free?

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