please rewrite sheetjs with es2015+ syntax

[anlexN]

i review sheetjs source code one line by one line, i think if it is written by es2015+, sheetjs size will be decreased by about 30%

[beeing]

Perhaps typescript would be better option? Would be interested to have a smaller bundle.

We can get more mileage if we focus on the cpexcel as its the largest part.

Noticed the cpexcel.js can probably be reduced in size as there's many repeated strings like we can have the common prefix as separate variable.

Below constant is repeated 31 times, which can reduce about 8K characters.

\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007\b\t\n\u000b\f\r\u000e\u000f\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~

The below scripts can be created as factory / common functions

Below is called 26 times - can reduce about 4K

, D = [], e = {}; for(var i=0;i!=d.length;++i) { if(d.charCodeAt(i) !== 0xFFFD) e[d.charAt(i)] = i; D[i] = d.charAt(i); } return {"enc": e, "dec": D }; })();

Below have 468 calls to it - about 50K reduction

for(j = 0; j != D[185].length; ++j) if(D[185][j].charCodeAt(0) !== 0xFFFD) { e[D[185][j]] = 47360 + j; d[47360 + j] = D[185][j];}

The above 3 combined, we can easily shave off 60K+ characters from the script.

I think the above should be still maintaining the readability of the current code.

[SheetJSDev]

@beeing the issue of a smaller codepage dependency will be tracked in the codepage repo

Preliminary ESM support has been pushed and some tree shaking is possible.