Looping through a List of objects in JavaScript

Question

I want to loop through the student list which I received from a REST service located on a server. this list contains objects for students enrolled in a section. Each object has firstName, lastName, student ID and many other attributes, specifically an attribute called isAbsent. Its a Boolean value where it has true if the student is absent and false if the student is present in not absent. I want to store the students IDs who are absent (have isAbsent=true) in another String Array.

I tried this :

{ 
    //this array will store the IDs of students who are absent.
    $scope.selection = [];
    //$scope.studentList is the list of students for CRN=X and Date=Y
    for (id in $scope.studentList) {
        if ($scope.studentList.isAbsent === true) {
            $scope.selection.push($scope.studentList.id);
            console.log($scope.selection);
        }
    }
}

This code doesn't execute. I have no clue why, I guess the problem in the loop structure. Any help?

Lee Taylor · Accepted Answer · 2014-06-07 16:11:50Z

3

Maybe this will help?

for (var i=0;i<$scope.studentList.length;i++)
{
    if ($scope.studentList[i].isAbsent === true) 
    {
        $scope.selection.push($scope.studentList[i].id);
        console.log($scope.selection);
    }
}

p.s. don't use for..in with arrays. It will display an index instead of a value. It's not like C#.

edited Jun 7, 2014 at 16:11

Lee Taylor

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answered Jun 7, 2014 at 15:43

Royi Namir

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4 Comments

Ali Khalil Over a year ago

It worked fine, but I need some clarifications: When I type studentList then followed by dot, I did not get the associated method "length" for this List. Does that mean we modified the prototype of the list?

Royi Namir Over a year ago

'm not sure i understand your question

Ali Khalil Over a year ago

I'm using Netbeans 8.0, I meant, that when I type studentList I expect to see dropdown suggestions list for the methods that are applied on this list, for example, studentList.getOwnPropertyNames() and studentList.defineProperty() which are suggestion by the IDE. However, the method studentList.length doesn't show up in this list of suggestions.

Royi Namir Over a year ago

IMHO netbeans is for java . not javascript. also - becuase $scope is a complex object ( very complex) - it's hard for autocomplete to realize that studentList is array.

Chris Montgomery · Accepted Answer · 2014-06-07 16:15:44Z

3

Depending on what browsers you need to support (e.g. IE >= 9), I'd suggest the newer foreach construct. I find it easier to use:

$scope.studentList.forEach(function(value, index, array) {
    if (value.isAbsent === true) 
    {
        $scope.selection.push(value.id);
        console.log($scope.selection);
    }
});

answered Jun 7, 2014 at 16:15

Chris Montgomery

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