Calculates the frequency of a note provided on 12TET scale. (traditional Western scale)

noteToFrequency.js

const a4Freq = 440;
const noteNames = ["A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#"];

function noteToFrequency(noteName) {
  const [, noteLetter, octaveNum] = noteName.match(/^(\w#?)(\d)$/) || [];
  const numStepsFromA = noteNames.indexOf(noteLetter.toUpperCase());
  if (numStepsFromA === -1 || !noteLetter) return new Error("Invalid note");
  
  const numStepsFromMiddleA = numStepsFromA + 12 * (octaveNum - 4);
  
  return a4Freq * (2**(1/12)) ** numStepsFromMiddleA;
}

// example

console.log(noteToFrequency("a#4"))

Not accurate. Works with A4-G#4 in octave 4 (where octave 4 actually should end with A4-B4, since note after is C5).