Question

我有两个属性，我需要为每个属性检查null和undefined，如何在if语句中使用它？

main.js

   var validateControlRating = function () {
            if ( ($scope.controlProcessRatingDTO.controlPerformanceRatingKey === null || 
                $scope.controlProcessRatingDTO.controlPerformanceRatingKey === undefined)
                &&
               ($scope.controlProcessRatingDTO.controlDesignRatingKey === null ||
                $scope.controlProcessRatingDTO.controlDesignRatingKey === undefined) ) {
              $scope.caculatedRatingDiv = false;
            } else {
            $http.get('app/control/rest/calculateControlEffectiveness/' + $scope.controlProcessRatingDTO.controlDesignRatingKey + '/' + $scope.controlProcessRatingDTO.controlPerformanceRatingKey).success(function (data) {
                $scope.calcaulatedRating = data;
            }, function (error) {
                $scope.statusClass ='status invalid userErrorInfo';
                var errorMessage = error.data.errorMsg;
                if (error.data.techErrorMsg) {
                    errorMessage = error.data.techErrorMsg;
                }
                $scope.statusInfo = errorMessage;
             });
            $scope.ratingValidationMsg = '';
            $scope.ratingWinValidationClass = 'valid';
            $scope.caculatedRatingDiv = true;
            $scope.enableRatingSave = false;
        }
    };

Answer 1

这在javascript中有点乏味，你必须编写每个条件，并使用括号等

 private void button19_Click(object sender, EventArgs e) //Loop button enables timer3 to start
    {
        timer3.Enabled = true;
        timer3.Interval = 401;
        timer3.Start();

        //sets vehicle mode to max speed 
        send_ok_flags |= 0x02; 
        sersendbuf[2] = 0x06;
        sersendbuf[3] = 0x13;
        sersendbuf[4] = 0x02;
        sersendbuf[5] = 0x00;
    }   

    private void button20_Click(object sender, EventArgs e) //stops timer 3
    {
        timer3.Stop(); 
        timer3.Enabled = false;
    }

    private void timer3_Tick(object sender, EventArgs e) //timer event
    {
        Int32.TryParse(maskedTextBox15.Text, out cDest);
        if (Math.Abs(cDest - dest) < 300) //close to target destination, go back to starting
        {
            button1.PerformClick();           
            counter++;
        }

        if (Math.Abs(cDest - sDest) < 300) //close to starting destination, go towards target 
        {
            send_ok_flags |= 0x02;
            byte[] s1buf = { 0xAB, 0xBA, 0x08, 0x12, 0x00, 0x00, 0x00, 0x00 };
            s1buf[4] = (byte)sDest;
            sDest >>= 8;
            s1buf[5] = (byte)sDest;
            sDest >>= 8;
            s1buf[6] = (byte)sDest;
            sDest >>= 8;
            s1buf[7] = (byte)sDest;
            s1buf.CopyTo(sersendbuf, 0);
            counter++;
        }

        label46.Text = counter.ToString();
        label47.Text = cDest.ToString();
        label48.Text = dest.ToString();
    }

或只是

if ( ($scope.controlProcessRatingDTO.controlPerformanceRatingKey === null || 
      $scope.controlProcessRatingDTO.controlPerformanceRatingKey === undefined)
      &&
     ($scope.controlProcessRatingDTO.controlDesignRatingKey === null ||
      $scope.controlProcessRatingDTO.controlDesignRatingKey === undefined) ) {...

Answer 2

我认为您需要检查此相关内容，检查undefined然后查看null 并使用&&而非||，因为您的代码将检查未定义变量的空值，这肯定会引发异常的码

if( typeof myVar == 'undefined' ? false: myVar ) { // go here defined and value not null }

或的码

if(typeof myVar != 'undefined' && myVar) { // go here defined and value not null }

在您的代码中，检查将像
一样
if ((typeof $scope.controlProcessRatingDTO.controlDesignRatingKey !== undefined|| typeof $scope.controlProcessRatingDTO.controlPerformanceRatingKey !== undefined) && ($scope.controlProcessRatingDTO.controlDesignRatingKey !== null || $scope.controlProcessRatingDTO.controlPerformanceRatingKey !== null)) { // do home work }else { // do other home work }

Answer 3

你也可以使用否定运算符，但这也会使“假”工作：

if (!$scope.controlProcessRatingDTO.controlPerformanceRatingKey && !$scope.controlProcessRatingDTO.controlDesignRatingKey) {

这有点短，但如果你想分别处理False值，那么请使用上面的Adeneo答案。

Answer 4

你可以这样做：

if ( some_variable == null ){
  // some_variable is either null or undefined
}

取自：How to check for an undefined or null variable in JavaScript?

如何检查null和undefined属性的两个值？

4 个答案: