How to filter from constructor function the array in it?

Question

I'm making a javascript course and I'm trying to create a function that filters from the array and removes a given value of it. NOTE: I've to use the filter() method.

I've tried several ways but without success. What am I doing wrong?

Here the code:

function Student(id, name, subjects = []) {
  this.id = id;
  this.name = name;
  this.subjects = subjects;  
}

Student.prototype.addSubject = function(subject) {
  this.subjects = [...this.subjects, subject];   
}

Student.prototype.removeSubject = function(remove) {
    this.subjects.filter(function(remove) {
        return this.subjects !== remove
    })
}

const student1 = new Student(1, 'Reed');

student1.addSubject('Math');
console.log(student1.subjects);
student1.removeSubject('Math');
console.log(student1.subjects)

Appreciate your time

filter doesn't modify the array, it returns a new one. this.subjects = this.subjects.filter(...) would fix the problem — malarres
– malarres, Commented Feb 25, 2022 at 10:23
Thanks for the response. I've added on the body of the function this.subjects = this.subjects.filter(function(remove)... but still get ['Math] when console.log — Zaesar
– Zaesar, Commented Feb 25, 2022 at 10:27
yes the filter needed some improvement. finally added as answer — malarres
– malarres, Commented Feb 25, 2022 at 10:27

malarres · Accepted Answer · 2022-02-25 10:25:57Z

2

filter doesn't modify the array, it returns a new one. this.subjects = this.subjects.filter plus a change in how you filter:

function Student(id, name, subjects = []) {
  this.id = id;
  this.name = name;
  this.subjects = subjects;  
}

Student.prototype.addSubject = function(subject) {
  this.subjects = [...this.subjects, subject];   
}

Student.prototype.removeSubject = function(remove) {
    this.subjects = this.subjects.filter(function(current) {
        return current !== remove
    })
}

const student1 = new Student(123,'pepe')

student1.addSubject('a');
student1.addSubject('Math');
student1.addSubject('b');
student1.addSubject('c');
console.log(student1.subjects);
student1.removeSubject('Math');
console.log(student1.subjects)

answered Feb 25, 2022 at 10:25

malarres

2,9481 gold badge24 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Zaesar Over a year ago

Yes! that's it. Appreciate you took the time to answer me so fast.

Tomalak · Accepted Answer · 2022-02-25 10:48:37Z

1

You can use .push() and .splice() to modify the subjects array in-place, instead of re-creating it for every modification, which a) is a waste and b) can cause difficult-to-find bugs.

But you absolutely should create a new array at the point of object creation, to avoid inadvertently modifying the subjects parameter outside during the lifetime of the Student instance.

function Student(id, name, subjects = []) {
  this.id = id;
  this.name = name;
  if (!Array.isArray(subjects)) throw new Error("subjects must be an array");
  this.subjects = [...subjects];
}

Student.prototype.addSubject = function (subject) {
  this.subjects.push(subject);   
}

Student.prototype.removeSubject = function (subject) {
  const pos = this.subjects.indexOf(subject);
  if (pos > -1) this.subjects.splice(pos, 1);
}

const student1 = new Student(1, 'Reed');

student1.addSubject('Math');
console.log(student1.subjects);
student1.removeSubject('Math');
console.log(student1.subjects)

edited Feb 25, 2022 at 10:48

answered Feb 25, 2022 at 10:31

Tomalak

339k68 gold badges547 silver badges635 bronze badges

2 Comments

malarres Over a year ago

the problem is that OP needs to use .filter() . must be a req from the course they're taking

Tomalak Over a year ago

@malarres I was on the fence about that, but it could be.

Collectives™ on Stack Overflow

How to filter from constructor function the array in it?

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related