quaggaJS/example/live_w_locator.js

$(function() {
    var App = {
        init : function() {
            Quagga.init({
                inputStream : {
                    name : "Live",
                    type : "LiveStream"
                },
                decoder : {
                    readers : ["upc_reader"]
                }
            }, function() {
                App.attachListeners();
                Quagga.start();
            });
        },
        attachListeners : function() {
            $(".controls .reader-group").on("change", "input", function(e) {
                e.preventDefault();
                Quagga.setReaders([e.target.value + "_reader"]);
            });

            $(".controls").on("click", "button.stop", function(e) {
                e.preventDefault();
                Quagga.stop();
            });
        },
        detachListeners : function() {
            $(".controls .reader-group").off("change", "input");
            $(".controls").off("click", "button.stop");
        },
        lastResult : null
    };

    App.init();

    Quagga.onProcessed(function(result) {
        var drawingCtx = Quagga.canvas.ctx.overlay,
            drawingCanvas = Quagga.canvas.dom.overlay;

        if (result) {
            if (result.boxes) {
                drawingCtx.clearRect(0, 0, parseInt(drawingCanvas.getAttribute("width")), parseInt(drawingCanvas.getAttribute("height")));
                result.boxes.filter(function (box) {
                    return box !== result.box;
                }).forEach(function (box) {
                    Quagga.ImageDebug.drawPath(box, {x: 0, y: 1}, drawingCtx, {color: "green", lineWidth: 2});
                });
            }

            if (result.box) {
                Quagga.ImageDebug.drawPath(result.box, {x: 0, y: 1}, drawingCtx, {color: "#00F", lineWidth: 2});
            }

            if (result.codeResult && result.codeResult.code) {
                Quagga.ImageDebug.drawPath(result.line, {x: 'x', y: 'y'}, drawingCtx, {color: 'red', lineWidth: 3});
            }
        }
    });

    Quagga.onDetected(function(result) {
        var code = result.codeResult.code;

        if (App.lastResult !== code) {
            App.lastResult = code;
            var $node = null, canvas = Quagga.canvas.dom.image;

            $node = $('<li><div class="thumbnail"><div class="imgWrapper"><img /></div><div class="caption"><h4 class="code"></h4></div></div></li>');
            $node.find("img").attr("src", canvas.toDataURL());
            $node.find("h4.code").html(code);
            $("#result_strip ul.thumbnails").prepend($node);
        }
    });

});