switchTab = function switchTab(windowHandle) {
    var _this = this;

    /*!
     * parameter check
     */
    if (typeof windowHandle !== 'string') {
        windowHandle = null;
    }

    if (windowHandle) {
        return this.window(windowHandle);
    }

    return this.windowHandles().then(function (tabIds) {
        if (tabIds && tabIds.value && tabIds.value.length) {
            return _this.switchTab(tabIds.value[0]);
        }
    });
}
Switch focus to a particular tab / window handle.

@alias browser.switchTab
@param {String=} windowHandle window handle URL to focus on (if no handle was specified the command switches to the first available one)
@uses protocol/window, window/getTabIds, window/switchTab
@type window