<div class="weui-cell__ft">
                    <input class="weui-switch" type="checkbox" id="btn-switch">
                </div>

var str = $("#btn-switch").is(":checked");

注：选中返回值：true；未选中返回值：false

                <div class="weui-cell__ft">
                    <input class="weui-switch" type="checkbox" id="btn-switch" checked="checked">
                </div>

                <div class="weui-cell__ft">
                    <input class="weui-switch" type="checkbox" id="btn-switch"/>
                </div>