javascript update all values in array of objects

Question

How to add a new property "comment" to all the students and return the ClassFoo?

ClassFoo = {
    "Total": 3, 
    "students": [
        {
            "name": "Peter",
            "grade": "C"
        },
        {
            "name": "Ben",
            "grade": "B"
        },
        {
            "name": "Ann",
            "grade": "B"
        },
    ]
};

Comments(B) = {
    "grade": "B",
    "comment": "Good"
};

Comments(C) = {
    "grade": "C",
    "comment": "Work harder"
};

Become like this

ClassFoo = {
    "Total": 3, 
    "students": [
        {
            "name": "Peter",
            "grade": "C",
            "comment": "Work harder"
        },
        {
            "name": "Ben",
            "grade": "B",
            "comment": "Good"
        },
        {
            "name": "Ann",
            "grade": "B",
            "comment": "Good"
        },
    ]
};

Should I create a new object? use .map for ClassFoo.students? and then match comments if Comments.grade === ClassFoo.students.grade, then .push comment?

Your syntax is not valid on line 2. Looks like ClassFoo it should be an {} object instead of an [] array. — CollinD
– CollinD, Commented Nov 6, 2018 at 20:37
do you want to get a new object or the same with mutated properties? why does Comments contain grade? — Nina Scholz
– Nina Scholz, Commented Nov 6, 2018 at 20:45

Callam · Accepted Answer · 2018-11-06 21:53:38Z

3

class ClassFoo {
  constructor(students) {
    this.total = students.length
    this.students = students
    this.students.forEach(student => {
      if (this.Comments[student.grade]) {
        student.comment = this.Comments[student.grade]
      }
    });
  }
  
  get Comments() {
    return {
      B: 'Good',
      C: 'Work Harder',
    }
  }
}

const classFoo = new ClassFoo([
  {
    "name": "Peter",
    "grade": "C"
  },
  {
    "name": "Ben",
    "grade": "B"
  },
  {
    "name": "Ann",
    "grade": "A"
  },
]);

console.log(classFoo)

edited Nov 6, 2018 at 21:53

answered Nov 6, 2018 at 20:39

Callam

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6 Comments

susu watari Over a year ago

What if I don't know what are the comments for different grade yet?

Callam Over a year ago

Well an E or an F in this example would result in an undefined comment, which is relatively representative of the grade if it doesn't have a comment yet. If you would prefer to leave out the comment if it is undefined, that can be done.

susu watari Over a year ago

Can it do Comments.grade === ClassFoo.students.grade ?

susu watari Over a year ago

I don't want to list out all the comments for grades

Callam Over a year ago

In that case, simply check if (this.Comments[student.grade]) is a truthy value before adding it to the student – I've updated that answer.

|

Willem van der Veen · Accepted Answer · 2018-11-06 22:16:10Z

0

You can use a for..of loop like this

ClassFoo = {
  "Total": 3,
  "students": [{
      "name": "Peter",
      "grade": "C"
    },
    {
      "name": "Ben",
      "grade": "B"
    },
    {
      "name": "Ann",
      "grade": "B"
    },
  ]
};

for (let student of ClassFoo.students) {

  if (student.grade === 'B') {
    student.comment = 'good';
  } else if (student.grade === 'C') {
    student.comment = 'work harder';
  }

}

console.log(ClassFoo)

A for..of loop will iterate over every element in the students array and add a property comment with the value of 'good' on a student object.

edited Nov 6, 2018 at 22:16

answered Nov 6, 2018 at 20:53

Willem van der Veen

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3 Comments

susu watari Over a year ago

what if I don't know what are the comment for grade? and students have different grades?

Willem van der Veen Over a year ago

Updated the answer, you can just put an if statement in your for of loop and in this way dynamically add comments based on the grade.

susu watari Over a year ago

if I have 24 grades, it is bad to list out all the conditions

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