Question

I have a JavaScript object as follows.

var sampleData = {
    "studentsList": {
        "Student1": {
            "marks": "123",
            "grade": "B"
        },
        "Student2": {
            "marks": "144",
            "grade": "A"
        }
    }
};​

Now the user enters the name of a student, say Student1 and I need to get the details of that object.

I have two questions.

[1] How do I get the details of the entered student using JavaScript?

When I use sampleData.studendsList.valueOf("Student1") returns me the complete object. I just need the details of “Student1”.

[2] Is this the correct way to do it? Or we should create an array of Students and that contains an property called “name” with value say Student1 ? If I go with this approach then I need to iterate through the entire array list to get the details of a student.

Which appraoch is better?

Answer 1

An array is usually the more natural way to store a list of items (like students). But there are tradeoffs. As structured (using objects), you can access any student by name in constant time:

sampleData.studentsList.Student1

Structuring with an array looks like this:

var sampleData = {
    "studentsList": [
        {
            "marks": "123",
            "grade": "B"
        },
        {
            "marks": "144",
            "grade": "A"
        }
    ]
};​

Access the nth student like this:

sampleData.studentsList[n]

If the index of the desired student is not known, then accessing a particular student (based on its details) is O(n) (because you’d need to iterate the entire array to find the correct item in the worst case).