How to transliterate Devanagari into Brahmi (mainly, diacritics)

Question

I have been messing around with converting a large Devanagari Sanskrit text to Brahmi using a simple mapping function. There is also this table showing how most of the characters map. I found one that doesn't though, the ऽ. Right now I'm just mapping it to अ, but please correct me if I'm wrong.

What I'm wondering about though is how to convert Sanskrit Devanagari text to Brahmi. Can I just strip the diacritics and call it a day? Or do I need to be more careful and look at (unicode) character combinations (like letter + diacritic) to map to a single (or perhaps multiple) Brahmi letter(s)? How do I convert Sanskrit Devanagari to Brahmi?

Right now I have this (the mapping is just what I wanted to show in case it's relevant):

var MAP = {
  "ऽ": "\u{11005}",
  "ॠ": "𑀌",
  "\u0905": "\u{11005}",
  "\u0906": "\u{11006}",
  "\u0907": "\u{11007}",
  "\u0908": "\u{11008}",
  "\u0909": "\u{11009}",
  "\u090A": "\u{1100A}",
  "\u090B": "\u{1100B}",
  "\u090C": "\u{1100D}",
  "\u090F": "\u{1100F}",
  "\u0910": "\u{11010}",
  "\u0913": "\u{11011}",
  "\u0914": "\u{11012}",
  "\u0915": "\u{11013}",
  "\u0916": "\u{11014}",
  "\u0917": "\u{11015}",
  "\u0918": "\u{11016}",
  "\u0919": "\u{11017}",
  "\u091A": "\u{11018}",
  "\u091B": "\u{11019}",
  "\u091C": "\u{1101A}",
  "\u091D": "\u{1101B}",
  "\u091E": "\u{1101C}",
  "\u091F": "\u{1101D}",
  "\u0920": "\u{1101E}",
  "\u0921": "\u{1101F}",
  "\u0922": "\u{11020}",
  "\u0923": "\u{11021}",
  "\u0924": "\u{11022}",
  "\u0925": "\u{11023}",
  "\u0926": "\u{11024}",
  "\u0927": "\u{11025}",
  "\u0928": "\u{11026}",
  "\u092A": "\u{11027}",
  "\u092B": "\u{11028}",
  "\u092C": "\u{11029}",
  "\u092D": "\u{1102A}",
  "\u092E": "\u{1102B}",
  "\u092F": "\u{1102C}",
  "\u0930": "\u{1102D}",
  "\u0932": "\u{1102E}",
  "\u0933": "\u{11034}",
  "\u0935": "\u{1102F}",
  "\u0936": "\u{11030}",
  "\u0937": "\u{11031}",
  "\u0938": "\u{11032}",
  "\u0939": "\u{11033}",
  "\u093E": "\u{11038}",
  "\u093F": "\u{1103A}",
  "\u0940": "\u{1103B}",
  "\u0941": "\u{1103C}",
  "\u0942": "\u{1103D}",
  "\u0943": "\u{1103E}",
  "\u0944": "\u{1103F}",
  "\u0962": "\u{11040}",
  "\u0963": "\u{11041}",
  "\u0947": "\u{11042}",
  "\u0948": "\u{11043}",
  "\u094B": "\u{11044}",
  "\u094C": "\u{11045}",
  "\u094D": "\u{11046}",
  "\u0964": "\u{11047}",
  "\u0965": "\u{11048}",
  "\u0966": "\u{11066}",
  "\u0967": "\u{11067}",
  "\u0968": "\u{11068}",
  "\u0969": "\u{11069}",
  "\u096A": "\u{1106A}",
  "\u096B": "\u{1106B}",
  "\u096C": "\u{1106C}",
  "\u096D": "\u{1106D}",
  "\u096E": "\u{1106E}",
  "\u096F": "\u{1106F}"
}

var combining = [
  '\u0900',
  '\u0901',
  '\u0902',
  '\u0903',
  '\u093a',
  '\u093b',
  '\u093c',
  '\u093e',
  '\u093f',
  '\u0940',
  '\u0941',
  '\u0942',
  '\u0943',
  '\u0944',
  '\u0945',
  '\u0946',
  '\u0947',
  '\u0948',
  '\u0949',
  '\u094a',
  '\u094b',
  '\u094c',
  '\u094d',
  '\u094e',
  '\u094f',
  '\u0955',
  '\u0956',
  '\u0957',
  '\uA8E0',
  '\uA8E1',
  '\uA8E2',
  '\uA8E3',
  '\uA8E4',
  '\uA8E5',
  '\uA8E6',
  '\uA8E7',
  '\uA8E8',
  '\uA8E9',
  '\uA8Ea',
  '\uA8Eb',
  '\uA8Ec',
  '\uA8Ed',
  '\uA8Ee',
  '\uA8Ef',
  '\uA8f0',
  '\uA8f1',
  '\u1CD1',
  '\u1CD4',
  '\u1CDb',
  '\u1CDe',
  '\u1CDf',
  '\u1Ce2',
  '\u1Ce3',
  '\u1Ce4',
  '\u1Ce5',
  '\u1Ce6',
  '\u1Ce7',
  '\u1Ce8',
  '\u1CF7',
]

var chars = []
for (var char of text) {
  char = char
    .replace(/\s+/g, '')
    .replace(/[\{\};\:\.,\"\'\(\)।॥\[\]]/g, '')
  if (!char) continue // ignore whitespace
  if (combining.includes(char)) continue // ignore diacritics?
  chars.push(MAP[char]) // brahmi character
}

What could I be doing better?

Note, I am wondering less about the code/technical aspects, and more about the linguistic aspect of orthography to orthography.