Example of pre-initialized AudioWorker proposal

main.js

var context = new AudioContext();
var sineWorker = context.createAudioWorker("worker.js");

function createSineNode (frequency) {
    var node = context.createAudioWorkerNode(sineWorker, {
        numberOfInputChannels: 0,
        numberOfOutputChannels: 1,
        parameters: {
            frequency: frequency || 440,
        },
    });

    node.start = function (time) {
        node.postMessage("start", { time: time });
    };
}

var node = createSineNode(220);

node.connect(context.destination);
node.start(1.2);

worker.js

var STATE_SILENCE = 0;
var STATE_WAITING_FOR_FIRST_FRAME = 1;
var STATE_PROCESSING = 2;

this.onaudionodecreated = function (event) {
    var node = event.node;
    var data = event.data;
    var phase = 0;
    var startTime = 0;
    var state = STATE_SILENCE;

    function process (frame, frequency, sampleRate) {
        for ( var i = 0; i < frame.length; i++ ) {
            frame[i] = Math.sin(phase * Math.PI * 2);
            phase = frequency[i] / sampleRate;
        }
    }

    node.onaudioprocess = function (event) {
        var frame = event.outputBuffers[0];
        var frequency = event.parameters.frequency;
        var sampleRate = event.sampleRate;

        switch ( state ) {
        case STATE_SILENCE:
            break;
        case STATE_WAITING_FOR_FIRST_FRAME:
            var startIndex = Math.floor(startTime * sampleRate);
            var frameIndex = Math.floor(event.playbackTime * sampleRate);
            if ( startIndex >= frameIndex + frame.length ) { return; }

            var firstIndex = startIndex - frameIndex;
            process(frame.subarray(firstIndex), frequency.subarray(firstIndex), sampleRate);
            break;
        case STATE_PROCESSING:
            process(frame, frequency, sampleRate);
            break;
        }
    };

    node.onmessage = function (event) {
        switch ( event.type ) {
        case "start":
            startTime = event.data.time;
            break;
        }
    };
};