index.ts

export type KeypadKey =
  | 0
  | 1
  | 2
  | 3
  | 4
  | 5
  | 6
  | 7
  | 8
  | 9
  | '1'
  | '2'
  | '3'
  | '4'
  | '5'
  | '6'
  | '7'
  | '8'
  | '9'
  | '0'
  | '#'
  | '*'
  | 'A'
  | 'B'
  | 'C'
  | 'D';

type WebAudioContext = {
  new (contextOptions?: AudioContextOptions | undefined): AudioContext;
  prototype: AudioContext;
};
declare global {
  interface Window {
    webkitAudioContext: WebAudioContext;
  }
}

class DTMF {
  oscillatorLow: OscillatorNode | undefined;
  oscillatorHigh: OscillatorNode | undefined;
  audioContext: AudioContext;

  constructor(audioContext?: AudioContext) {
    const AudioContext = window.AudioContext || window.webkitAudioContext;
    this.audioContext = audioContext || new AudioContext();
  }

  createOscillator({
    frequency,
    type = 'sine',
  }: {
    frequency: number;
    type?: OscillatorType;
  }): OscillatorNode {
    let oscillator = this.audioContext.createOscillator();
    oscillator.frequency.value = frequency;
    oscillator.type = type;
    return oscillator;
  }

  playTone(lowFrequency: number, highFrequency: number): void {
    this.stop();
    let gainNode = this.audioContext.createGain();
    gainNode.gain.value = 0.1;

    this.oscillatorLow = this.createOscillator({ frequency: lowFrequency });
    this.oscillatorLow.connect(gainNode, 0, 0);
    gainNode.connect(this.audioContext.destination);

    this.oscillatorHigh = this.createOscillator({ frequency: highFrequency });
    this.oscillatorHigh.connect(gainNode);
    gainNode.connect(this.audioContext.destination);

    this.oscillatorLow.start(0);
    this.oscillatorHigh.start(0);
  }

  private playKey(key: KeypadKey): void {
    switch (String(key)) {
      case '1':
        this.playTone(697, 1209);
        break;
      case '2':
        this.playTone(697, 1336);
        break;
      case '3':
        this.playTone(697, 1477);
        break;
      case '4':
        this.playTone(770, 1209);
        break;
      case '5':
        this.playTone(770, 1336);
        break;
      case '6':
        this.playTone(770, 1477);
        break;
      case '7':
        this.playTone(852, 1209);
        break;
      case '8':
        this.playTone(852, 1336);
        break;
      case '9':
        this.playTone(852, 1477);
        break;
      case '*':
        this.playTone(941, 1209);
        break;
      case '0':
        this.playTone(941, 1336);
        break;
      case '#':
        this.playTone(941, 1477);
        break;
      case 'A':
        this.playTone(697, 1633);
        break;
      case 'B':
        this.playTone(770, 1633);
        break;
      case 'C':
        this.playTone(852, 1633);
        break;
      case 'D':
        this.playTone(941, 1633);
        break;
    }
  }

  play(key: KeypadKey): void {
    this.playKey(key);
  }

  stop(): void {
    if (this.oscillatorLow) {
      this.oscillatorLow.disconnect();
    }
    if (this.oscillatorHigh) {
      this.oscillatorHigh.disconnect();
    }
  }

  close(): void {
    if (this.audioContext) {
      this.audioContext.close();
    }
  }
}

export default DTMF;