How can I use a forEach method for or any array methods for Objects of arrays in Javascript?

Question

I'm learning to use modern array methods on arrays, but is there a way I can use these methods on objects of arrays? If not is it better to store the entire object into an array?

var course = {
  name: "My Javascript Tutorial",
  awesome: true,
  teachers: ["Brandon", "Shane", "Mike"],
  students: [
    {
      name: "Cliff",
      computer: {
        OS: "macOS",
        type: "iMac"
      }
    },
    {
      name: "Arthur",
      computer: {
        OS: "macOS",
        type: "Macbook Pro"
      }
    },
    {
      name: "Donald",
      computer: {
        OS: "macOS",
        type: "Windows PC"
      }
    }
  ]
};


course.forEach(function(item){
    console.log(course.students[item].name + 'uses a ' + course.students[item].computer.type);
})

This is the Error I'm getting.

TypeError: Cannot read property 'students' of undefined

CertainPerformance · Accepted Answer · 2019-09-01 22:07:30Z

The array you want to iterate over is course.students, so reference course.students and call forEach on it.

The first argument to forEach will be the item being iterated over (an element of the array). Because your elements are objects, reference their name and computer properties to log them properly:

var course = {
  name: "My Javascript Tutorial",
  awesome: true,
  teachers: ["Brandon", "Shane", "Mike"],
  students: [
    {
      name: "Cliff",
      computer: {
        OS: "macOS",
        type: "iMac"
      }
    },
    {
      name: "Arthur",
      computer: {
        OS: "macOS",
        type: "Macbook Pro"
      }
    },
    {
      name: "Donald",
      computer: {
        OS: "macOS",
        type: "Windows PC"
      }
    }
  ]
};


course.students.forEach(function(item){
    console.log(item.name + 'uses a ' + item.computer.type);
})

Mohit Dhingra · Accepted Answer · 2019-09-03 06:15:11Z

1

forEach() function call is supported only for the arrays, not for the objects.

In your case, if you want to traverse the array students, then you have to first get the reference to the students array from the course object.

This is how you can proceed:

    course.students.forEach(function(item){
console.log(item.name + 'uses a ' + item.computer.type); })

edited Sep 3, 2019 at 6:15

answered Sep 2, 2019 at 8:09

Mohit Dhingra

113 bronze badges

2 Comments

Borja Over a year ago

please also insert the last key and parenthesis '})' in the code snippet, thanks

Mohit Dhingra Over a year ago

Done :) @borchvm

EugenSunic · Accepted Answer · 2019-09-01 22:07:45Z

0

If you want to loop through your students array inside the object then you have to use indexes in the array, hence add an i variable in the foreEach

course.students.forEach(function(item, i) {
    console.log(course.students[i].name + 'uses a ' + course.students[i].computer.type);
})

Or just use the object/item and display the properties of that object in every iteration

course.students.forEach(function (item) {
  console.log(item.name + 'uses a ' + item.computer.type);
})

answered Sep 1, 2019 at 22:07

EugenSunic

13.8k15 gold badges68 silver badges96 bronze badges

Comments

Julian · Accepted Answer · 2019-09-01 22:12:24Z

0

The problem is, that you are trying to use the forEach loop on a object, which is not supported. Next you have the problem that you are trying to call the student name inside of a function, where it can't find the value course directly.

What you can do is following:

course.students.forEach(function(student) {
    console.log(student.name); 
});

answered Sep 1, 2019 at 22:12

Julian

3,90111 gold badges43 silver badges72 bronze badges

1 Comment

xZile Over a year ago

excellent response thank you, allowed me to write course.students.forEach(function(student){ console.log(student.name + 'uses a ' + student.computer.type); });

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