javascript - 日期对象的行为不符合预期

Question

我有一个控件，可以在我的应用程序开始时显示当前月份和年份。它有 2 个按钮，可以将当前月份加或减 1。我使用相同的函数来加/减，通过用 0 调用它来初始化日期。函数如下:

$scope.SetDateMonth = function (modifier) {
        if (modifier === 0) {
            //initialize the current date, only called on load
            $scope.CurrentDate = new Date();

        } else {
            //alter the currentdate
            $scope.CurrentDate.setMonth($scope.CurrentDate.getMonth() + modifier);
        }
        /*
        $scope.StartOfRange = new Date($scope.CurrentDate.getFullYear(), $scope.CurrentDate.getMonth());
        alert($scope.StartOfRange.getDate());
        $scope.StartOfRange.setDate(1);
        alert($scope.StartOfRange.getDate());
        //$scope.StartOfRange.setDate(1);
        $scope.EndOfRange = new Date($scope.CurrentDate.getFullYear(), $scope.CurrentDate.getMonth()+1);
        $scope.EndOfRange.setDate($scope.EndOfRange.getDate() - 1);
       */

        //set startofrange to first day of month
        $scope.StartOfRange = new Date($scope.CurrentDate.getFullYear(), $scope.CurrentDate.getMonth(), 1);
        //this sets the date to the last day of the previous month. Bc. we add 1 to the month, this will result in the last day of CurrentMonth
        $scope.StartOfRange = new Date($scope.CurrentDate.getFullYear(), $scope.CurrentDate.getMonth()+1, 0); 

        console.log("Start");
        console.log($scope.StartOfRange);
        console.log("End");
        console.log($scope.EndOfRange);

        //.setHours(0,0,0,0)

        //$scope.DateChanged();
    }

我想为此添加 2 个全局变量。范围开始/结束。他们必须存储该月的第一天和最后一天。您可以看到相当多的代码已被注释掉，我一直在尝试在网上找到的很多不同的示例。我被困在 setDate() (也许它不再在我提供的代码中，我确实尝试使用它但无法让它工作)函数。如果我用参数 1 调用它，它会将日期设置为 30。我也尝试过 UTC 时间。

奇怪的是，当我使用警报时，它按预期显示 1。当我使用 console.log 时，它没有。我尝试了从 1 到 30 的所有值，它们都给出了模糊的意外结果。

从 w3 ( https://www.w3schools.com/jsref/jsref_obj_date.asp ) 读取，我正确地调用了它。我确实设法通过构造一个新的日期对象来获取正确的日期，其中日期(或日期，有点令人困惑，第三个参数)设置为-29。似乎始终将日期设置为 1，但绝对不是长期解决方案。

Answer 1

您可以使用以下两个函数来查找当月的第一天和最后一天。

$scope.StartOfRange = $scope.getFirstDay();    
$scope.EndOfRange = $scope.getLastDay();
$scope.getFirstDay = function ()
{
    var currDate = new Date();     
    year = currDate.getFullYear();
    month = currDate.getMonth();
    day = currDate.getDate();
    var lastMonth = month - 1;
    if (month == 0) {
        year--;
        lastMonth = 11;
    }
    lastDay = 28;
    var previousMonthDate = new Date(year, lastMonth,lastDay);

    while (previousMonthDate < currDate)
    {
        previousMonthDate = new Date(year, lastMonth, lastDay++);
        var curMonth = previousMonthDate.getMonth();
        if (curMonth == month)
        {
            console.log("First Day :" + previousMonthDate);
            return previousMonthDate;
        }
    }
}
$scope.getLastDay = function () {
    var currDate = new Date();
    year = currDate.getFullYear();
    var nextYear = year;
    month = currDate.getMonth();
    day = currDate.getDate();
    var nextMonth = month + 1;
    if (month == 11) {
        nextYear++;
        nextMonth = 0;
    }
    lastDay = 28;
    var currentMonthDate = new Date(year, month, lastDay);
    var nextMonthDate = new Date(nextYear, nextMonth, 1);
    while (currentMonthDate < nextMonthDate) {
        var finalDate = currentMonthDate;
        currentMonthDate = new Date(year, month, lastDay++);
        var curMonth = currentMonthDate.getMonth();
        if (curMonth == nextMonth) {
            console.log("LastDay :" + finalDate);
            return finalDate;
        }
    }
}