mui两种退出应用的方式：

//1.1
var backButtonPress = 0;
$.back = function(event) {
    backButtonPress++;
    if(backButtonPress > 1) {
        plus.runtime.quit();
    } else {
        plus.nativeUI.toast('再按一次退出应用');
    }
    setTimeout(function() {
        backButtonPress = 0;
    }, 1000);
    return false;
};

//1.2
mui.back = function() {
    var btn = ["确定", "取消"];
    mui.confirm('确认关闭当前窗口？', 'Hello MUI', btn, function(e) {
        if(e.index == 0) {
            plus.runtime.quit();
        }
    });
}