create object property by assign value in a for loop

Question

In this excercise I create 3 function. score() to generate a random Number. generateStudents() to create a list Object. Object has format {student:'name',marks:{...}} as define in generateStudents(). In last function, I create obj and obj1. obj is a list (assign value equal to function 2) and obj1 has format {"subject":...,"student_score:{}}.

I assign key:value in a for loop to create the property "student_score" (also an object) but when i get out of for loop and print obj1 it does not include the part i have assign in for loop.

How can i assign key:value for a property (also an object) using for loop?

var score = function getRandomMark(start, end, step) {

    var num = start
    var arr = []
    arr.push(num)
    while (num <= (end - step)) {
        num += step
        arr.push(num)
    }
    var index = Math.floor(Math.random() * (arr.length))


    return (arr[index])
}
var generateStudents = function generateStudent(nameArr) {
    var studentArr = []
    for (let i = 0; i < nameArr.length; i++) {
        var student = {
            "name": nameArr[i],
            "marks": {
                "literature": score(6, 10
                    , 0.5),
                "maths": score(6, 10
                    , 0.5),
                "chemistry": score(6, 10
                    , 0.5),
                "history": score(6, 10
                    , 0.5),
                "biology": score(6, 10
                    , 0.5)
            }
        }
        studentArr.push(student)

    }
    return studentArr
}
var markList = ["Chi", "Duc", "Huy"]

var findStudentMinMax = function findStudentMinMax() {

    var obj = generateStudents(markList)
    console.log(typeof (obj))

    var obj1 = {}

    var arr1 = []

    const keys1 = Object.keys(obj[0]["marks"])

    for (let i = 0; i < keys1.length; i++) {

        var name = obj[0]["name"]

        var markObj = obj[0]["marks"]
        obj1["subject"] = keys1[i]
        obj1["student_score"] = {}
        //get all subject 
        for (let i = 0; i < obj1.length; i++) {

            obj1["student_score"][name] = markObj[obj1["subject"]]


        }


        console.log(obj1)
        arr1.push(obj1)


    }




}
findStudentMinMax()

Answer 1

I've made a few changes to the code inside findStudentMinMax.

• Changed obj to students as it makes the code easier to understand.
• Used j in the inner for loop as it was clashing with the i being used in the outer loop.
• Used students.length instead of obj1.length in the inner loop as I believe we're trying to loop through the students.
• Found the student name and marks in the inner loop, as that's where we're going through each student.

var score = function getRandomMark(start, end, step) {

    var num = start
    var arr = []
    arr.push(num)
    while (num <= (end - step)) {
        num += step
        arr.push(num)
    }
    var index = Math.floor(Math.random() * (arr.length))


    return (arr[index])
}
var generateStudents = function generateStudent(nameArr) {
    var studentArr = []
    for (let i = 0; i < nameArr.length; i++) {
        var student = {
            "name": nameArr[i],
            "marks": {
                "literature": score(6, 10
                    , 0.5),
                "maths": score(6, 10
                    , 0.5),
                "chemistry": score(6, 10
                    , 0.5),
                "history": score(6, 10
                    , 0.5),
                "biology": score(6, 10
                    , 0.5)
            }
        }
        studentArr.push(student)

    }
    return studentArr
}
var markList = ["Chi", "Duc", "Huy"]

var findStudentMinMax = function findStudentMinMax() {

    var students = generateStudents(markList) // changed name of obj to students to make things clearer
    // console.log(typeof (obj))

    var obj1 = {}

    var arr1 = []

    const keys1 = Object.keys(students[0]["marks"])

    for (let i = 0; i < keys1.length; i++) {

        // var name = obj[0]["name"]
        // var markObj = students[0]["marks"]
        
        obj1["subject"] = keys1[i]
        obj1["student_score"] = {}
        //get all subject 
        for (let j = 0; j < students.length; j++) { // j instead of i
            let name = students[j]["name"]; // getting name from students
            let markObj = students[j]["marks"] // getting markObj from students

            obj1["student_score"][name] = markObj[obj1["subject"]]


        }


        console.log(obj1)
        arr1.push(obj1)


    }




}
findStudentMinMax()

Answer 2

It seems that the i < obj1.length; always returns false. Hence your for loop never runs. You can never access .length on an object so you have to change the for loop to i < Object.keys(obj1).length. I am still not sure what you want your output object to be because you only stated you wanted to insert the value inside the object. Please find below the runnable code snippet.

var score = function getRandomMark(start, end, step) {

    var num = start
    var arr = []
    arr.push(num)
    while (num <= (end - step)) {
        num += step
        arr.push(num)
    }
    var index = Math.floor(Math.random() * (arr.length))


    return (arr[index])
}
var generateStudents = function generateStudent(nameArr) {
    var studentArr = []
    for (let i = 0; i < nameArr.length; i++) {
        var student = {
            "name": nameArr[i],
            "marks": {
                "literature": score(6, 10
                    , 0.5),
                "maths": score(6, 10
                    , 0.5),
                "chemistry": score(6, 10
                    , 0.5),
                "history": score(6, 10
                    , 0.5),
                "biology": score(6, 10
                    , 0.5)
            }
        }
        studentArr.push(student)

    }
    return studentArr
}
var markList = ["Chi", "Duc", "Huy"]

var findStudentMinMax = function findStudentMinMax() {

    var obj = generateStudents(markList)
    console.log(typeof (obj))

    var obj1 = {}

    var arr1 = []

    const keys1 = Object.keys(obj[0]["marks"])

    for (let i = 0; i < keys1.length; i++) {

        var name = obj[0]["name"]

        var markObj = obj[0]["marks"]
        obj1["subject"] = keys1[i]
        obj1["student_score"] = {}
        //get all subject 
        for (let i = 0; i < Object.keys(obj1).length; i++) {

            obj1["student_score"][name] = markObj[obj1["subject"]]


        }


        console.log(obj1)
        arr1.push(obj1)


    }




}
findStudentMinMax()