getting student marks with types by combining three arrays but returned a function is a string

Question

I have three arrays: students, type, and marks. I want to combine these into one array called student_marks to get each student's marks with mark types. But the object mark function is returned as a string and is not executed in javascript as shown in the picture code result.

I want to get this result:

 {student: '2'; totalmarks: '0'; mark: {'typeid'="marks" ,'typeid'="marks" , 'typeid'="marks" }}

So as a whole the result array which is student_marks will look like:

 {student: '2'; totalmarks: '0'; mark: {'1'="1" ,'2'="2" , '3'="3" }}
 {student: '3'; totalmarks: '0'; mark: {'1'="5" ,'2'="4" , '3'="7" }}
 {student: '4'; totalmarks: '0'; mark: {'1'="8" ,'2'="7" , '3'="9" }}

Here is my code sample is written in js:

   let std = [
  1, 2, 3, 4
];

let marks = [{
    type: '2',
    marks: '2'
  }, {
    type: '1',
    marks: '1'
  },
  {
    type: '3',
    marks: '3'
  }, {
    type: '2',
    marks: '2'
  },
  {
    type: '1',
    marks: '1'
  }, {
    type: '3',
    marks: '3'
  },
  {
    type: '2',
    marks: '2'
  }, {
    type: '1',
    marks: '1'
  },
  {
    type: '3',
    marks: '3'
  }, {
    type: '2',
    marks: '2'
  },
  {
    type: '1',
    marks: '1'
  }, {
    type: '3',
    marks: '3'
  }
];

let type = [2, 1, 3];
let ri = 0;
let student_marks = [];
let registrationIds = [];
let total_marks = [];
std.forEach(item => {

  registrationIds[ri] = item;


  // type[ri]=marks[ri];

  // marks:marks[ri];
  student_marks.push({
    student: item,

    mark: () => {

      for (let i = 0; i < marks_type.length; i++) {
        // m[marks_type[i]]=marks[i][ri];
        m = [{
          type: marks_type[i],
          marks: marks[i]['marks'],

        }];
        // m:{
        //     marks_type[i]=marks[i][ri];
        // };
      }
      console.log(m);
      return m;
    },


    //  totalmarks: total_marks[ri].value,
  });


  //  totalmark[ri]=total_marks[ri].value;




  ri++;
});

console.log(student_marks);

Answer 1

Since JavaScript functions are first class citizens, meaning it is treated similar to variables, the function in mark inside the object student_marks is assigned to it and not executed. Also note that the returned value is a function which you have mentioned a string. For your code to work,

• Method 1:

Wrap that function somewhere and just call it instead.

const calculateMark =  () => {
  for (let i = 0; i < marks_type.length; i++) {
    // m[marks_type[i]]=marks[i][ri];
    m = [{
      type: marks_type[i],
      marks: marks[i]['marks'],
    }];
    // m:{
    //     marks_type[i]=marks[i][ri];
    // };
  }
  console.log(m);
  return m;
};

student_marks.push({
  student: item,
  mark: calculateMark()
  //  totalmarks: total_marks[ri].value,
  });

• Method 2:

Use IIFE

student_marks.push({
  student: item,
  mark: (() => {
    for (let i = 0; i < marks_type.length; i++) {
      // m[marks_type[i]]=marks[i][ri];
      m = [{
        type: marks_type[i],
        marks: marks[i]['marks'],
      }];
      // m:{
      //     marks_type[i]=marks[i][ri];
      // };
    }
    console.log(m);
    return m;
  })(),
  //  totalmarks: total_marks[ri].value,
  });