If you like provided functionality, you should give a look to my Chrome Extension which provides same functions without the need to enter anything into the Developer Console. You can get the extension here: https://chrome.google.com/webstore/detail/battlelog-emblem-editor-e/noagedoiolkfaoaknohhepocfeooibjb

bf4-emblem-editor-extender.js

var fitAngle = function(angle) {
    return angle < 0 ? angle + 360 : angle;
}

function mirrorx() {
    var object = emblem.emblem.canvas.getActiveObject(),
        angle = object.get('angle');

    object.set('angle', fitAngle(-object.get('angle')));
    object.set('flipY', !object.get('flipY'));

    emblem.emblem.render();
}

function mirrory() {
    var object = emblem.emblem.canvas.getActiveObject();

    object.set('angle', fitAngle(180 - object.get('angle')));
    object.set('flipY', !object.get('flipY'));

    emblem.emblem.render();
}

function centerize() {
    var object = emblem.emblem.canvas.getActiveObject(),
        center = emblem.emblem.canvas.getCenter();

    object.set('left', center.left);
    object.set('top', center.top);
    object.setCoords();

    emblem.emblem.render();
}

(function() {
    var layerActions = $('div.layer-actions');

    //  Add mirroring buttons to action bar
    layerActions.append('<button class="btn" onclick="mirrorx();">MX</button>');
    layerActions.append('<button class="btn" onclick="mirrory();">MY</button>');
    layerActions.append('<button class="btn" onclick="centerize();">C</button>');

    //  Layer information (pos, angle, scale)
    $('div.emblem-layer-options')
        .after('<div id="layer-angle"></div>')
        .after('<div id="layer-size"></div>')
        .after('<div id="layer-pos"></div>');

    var pos = $('div#layer-pos'),
        size = $('div#layer-size'),
        angle = $('div#layer-angle');

    //  Info updater
    var intervalMs = 1000 / 10;

    window.setInterval(function () {
        var object = emblem.emblem.canvas.getActiveObject();

        if (!object) {
            pos.html('');
            size.html('');
            angle.html('');
            return;
        }

        pos.html('Position: ' + object.get('left').toFixed(2) + ' : ' + object.get('top').toFixed(2));
        size.html('Size: ' + object.getWidth().toFixed(2) + ' : ' + object.getHeight().toFixed(2));
        angle.html('Angle: ' + object.get('angle').toFixed(2));

        //  decrease 'corner' size a bit
        var cornerSize = Math.min(12, Math.max(4, Math.sqrt(object.getWidth() * object.getHeight()) / 10));
        if (object.getCornerSize() != cornerSize) {
            object.setCornerSize(cornerSize);
            emblem.emblem.render();
        }
    }, intervalMs);

    // Set background image
    $('canvas#emblem-canvas')
        .css('background-image', 'url(image.url)')
        .css('background-size', 'contain')
        .css('background-position', 'center')
        .css('background-repeat', 'no-repeat');
})();