How to modify a key in an array of objects by its index?

Question

I am working on React. I've created a Class to create a training program. In function of the training frequency number n selected by the user I need to create 1,2..n training programs. This is the class I created:

class Training {
  km = 0;
  programNum = 1;
  success = false;
  constructor(frequency, years) {
    this.frequency = frequency;
    this.years = years;
  }
}

This is the function for the training program:

const createTraining = (frequency, years) => {
    const newTraining = new Training(frequency, years);
    var temp = [];
    for (var i = 0; i < frequency; i++) {
      temp.push(newTraining);
    }}

 temp.forEach((item, i) => {
      item.programNum = i + 1;
    });
  console.log(temp);


// For frequency=4, it creates an array of 4 trainings:
(4) [Training, Training, Training, Training]
0: Training {km: 0, programNum: 4, success: false, frequency: '4', years: '2'}
1: Training {km: 0, programNum: 4, success: false, frequency: '4', years: '2'}
2: Training {km: 0, programNum: 4, success: false, frequency: '4', years: '2'}
3: Training {km: 0, programNum: 4, success: false, frequency: '4', years: '2'}
length: 4

Inside this array I would like to assign 1,2,3,4 so I user forEach but instead it assigns 4,4,4,4 to the key programNum I would like it to be like this:

(4) [Training, Training, Training, Training]
0: Training {km: 0, programNum: 1, success: false, frequency: '4', years: '2'}
1: Training {km: 0, programNum: 2, success: false, frequency: '4', years: '2'}
2: Training {km: 0, programNum: 3, success: false, frequency: '4', years: '2'}
3: Training {km: 0, programNum: 4, success: false, frequency: '4', years: '2'}
length: 4

I can't figure out how to do that.

it could be as easy as array.forEach((training, i) => obj.programNum= i);? or maybe just set that property before pushing each object in the resulting array. Or maybe even having it as an optional argument in the constructor. And last one :) you may model your own list of Training type. So that it owns the logic to flip the programNum when you add trainings to the list. — Diego D
– Diego D, Commented Jan 5, 2023 at 11:32
I have edited my question. I used temp.forEach((item, i) => {item.programNum = i + 1 })but it does not give 1,2,3,4 it assigned the length instead... — Yehoudith Polony
– Yehoudith Polony, Commented Jan 5, 2023 at 11:36

Adam Fanslau · Accepted Answer · 2023-01-05 11:42:42Z

1

The problem is that your pushing a reference to the same object 4 times. Do this instead:

const createTraining = (frequency, years) => {

    for (var i = 0; i < frequency; i++) {
        const newTraining = new Training(frequency, years);
        newTraining.programNum = i + 1;
        temp.push(newTraining);

    }
}

answered Jan 5, 2023 at 11:42

Adam Fanslau

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Comments

jkim · Accepted Answer · 2023-01-05 12:04:07Z

0

A small modification to the executable statement should give you the desired functionality.

// your code
class Training {
  km = 0;
  programNum = 1;
  success = false;
  constructor(frequency, years) {
    this.frequency = frequency;
    this.years = years;
  }
}

// slightly modified code
const createTraining = (frequency, years) => {
  let temp = [];

  for (let i = 0; i < frequency; i++) {
    const newTraining = new Training(frequency, years);
    newTraining.programNum += i;
    temp.push(newTraining);
  }

  return temp;
};

// test result
const result = createTraining(4, 2);
console.log(result);

answered Jan 5, 2023 at 12:04

jkim

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