I'm trying to use the Web Audio API in JavaScript to load a sound into a buffer and play it. Unfortunately it doesn't work and I get the following error:

Uncaught TypeError: Failed to set the 'buffer' property on 'AudioBufferSourceNode':

The provided value is not of type 'AudioBuffer'.

I can pinpoint which line is giving me the error, but I don't know why. Here is the relevant code if it helps:

var audioContext;

var playSoundBuffer;



function init() {

    window.AudioContext = window.AudioContext || window.webkitAudioContext;

    audioContext = new AudioContext();



    loadNote();

}



function loadNote() {

    var request = new XMLHttpRequest();

    request.open(GET, ./sounds/topE.wav, true);

    request.responseType = arraybuffer;

    request.onload = function() {

        audioContext.decodeAudioData(request.response, function(buffer) {

            playSoundBuffer = buffer;

        }, function(error) {

            console.error(decodeAudioData error, error);

        });

    };

    request.send();



    playSound();

}



function playSound() {

    var source = audioContext.createBufferSource();

    source.buffer = playSoundBuffer;       // This is the line that generates the error

    source.connect(audioContext.destination);

    source.start(0);

}

I believe the decodeAudioData method returns an AudioBuffer to its first callback function (its second parameter). I tried to save this AudioBuffer to the playSoundBuffer and then play it, but I get that error and I'm not sure why. Any help would be greatly appreciated.