audio-button.js

function toggleAudio (event, audioId, buttonId) {
    event.preventDefault();

    var audio  = document.getElementById(audioId);
    var button = document.getElementById(buttonId);

    if (audio.paused) {
        audio.play();
        button.classList.add('playing');
        button.classList.remove('paused');
    } else if (!audio.paused || audio.currentTime) {
        audio.pause();
        button.classList.add('paused');
        button.classList.remove('playing');
    } else {
        audio.play();
        button.classList.add('paused');
        button.classList.remove('playing');
    }
}