[JS] Easier way to work with decimals

[asfimport]

I have table with a column, let’s call the column c. c.type returns Decimal {scale: 3, precision: 12}. c.get(0) returns [519500, 0, 0, 0]. I know the value should be 519.5. After much digging, I found that the value is actually an arrow “big number” (https://github.com/apache/arrow/blob/ccdbbe3b765d4df9b2b91270a69ad78a086f2d77/js/src/util/bn.ts), so it has a valueOf function which returns 519500 (with the obvious caveat that it’ll overflow if the number is more than 53-bits). I could divide that by 10^scale from c.type to get 519.5. Is there some easier way to do that?

Filed by bmatcuk@gmail.com

Reporter: Dominik Moritz / @domoritz

_{Note: This issue was originally created as ARROW-13099. Please see the migration documentation for further details.}