下面的代码截取一个屏幕截图，并切断作为css选择器传递的某个元素。

const imageLib = require('imagelib/imageLib');

withoutElementScreenshot.prototype.command = function (selector, filename, cb) {
    var self = this;

    function execute(client, selector, filename, cb) {
        client.element('css selector', selector, function (element) {
            client.elementIdLocationInView(element.value.ELEMENT, function (location) {
                client.elementIdSize(element.value.ELEMENT, function (size) {
                    client.takeScreenshot(filename, function () {
                        imageLib(filename).pngToData(function () {
                            for (var x = location.value.x; x < size.value.width + location.value.x; x++) {
                                for (var y = location.value.y; y < size.value.height + location.value.y; y++) {
                                    this.setPixel(x, y, 255, 255, 255, 255);
                                }
                            }
                            this.toPng(filename, function () {
                                client.log('Screenshot without element would be saved into ' + filename);
                                cb();
                            });
                        });
                    });
                });
            });
        });
    }

如何传递选择器数组以将其全部切断？我无法遍历数组，因为takescreenshot函数位于回调之间。