oscillator experiment

simple_synth.js

(() => {
  const audioCtx = new (window.AudioContext || window.webkitAudioContext)();

  const noteMap = {
      '90': {
          key: 'Z',
          note: 'C',
          freq: 261.63
      },
      '83': {
          key: 'S',
          note: 'C#',
          freq: 277.18
      },
      '88': {
          key: 'X',
          note: 'D',
          freq: 293.66
      },
      '68': {
          key: 'D#',
          note: 'C',
          freq: 311.13
      },
      '67': {
          key: 'E',
          note: 'C',
          freq: 329.63
      },
      '86': {
          key: 'V',
          note: 'F',
          freq: 349.23
      },
      '71': {
          key: 'G',
          note: 'F#',
          freq: 369.99
      },
      '66': {
          key: 'G',
          note: 'F',
          freq: 392.00
      },
      '72': {
          key: 'H',
          note: 'G#',
          freq: 415.30
      },
      '78': {
          key: 'N',
          note: 'A',
          freq: 440.00
      },
      '74': {
          key: 'J',
          note: 'A#',
          freq: 466.16
      },
      '77': {
          key: 'B',
          note: 'F',
          freq: 493.88
      },
      '188': {
          key: ',',
          note: 'C',
          freq: 523.25
      },
  };

  const pressedKeys = {};

  const createOscillator = (noteObject) => {
      const oscillator = audioCtx.createOscillator();

      oscillator.frequency.setValueAtTime(noteObject.freq, audioCtx.currentTime); // value in hertz
      oscillator.connect(audioCtx.destination);
      oscillator.start();
      return oscillator;
  }

  const playNote = (e) => {
      const {keyCode} = e;
      const avilableKeys = Object.keys(noteMap);
      const inNoteMap = avilableKeys.some(key => key == keyCode);
      const inPressedKeys = pressedKeys[keyCode];
      if (inNoteMap && !inPressedKeys) {
          const noteObject = noteMap[keyCode];
          pressedKeys[keyCode] = createOscillator(noteObject);
      }
  }

  const stopNote = (e) => {
      const {keyCode} = e;
      const avilableKeys = Object.keys(noteMap);
      const inNoteMap = avilableKeys.some(key => key == keyCode);
      if (inNoteMap) {
          const oscillator = pressedKeys[keyCode];
          oscillator.stop();
          delete pressedKeys[keyCode];
      }
  }


  document.body.addEventListener('keydown', playNote);
  document.body.addEventListener('keyup', stopNote);

})()