Adding a new element to an object in an array

Question

Lets say I have and array made up of objects:

var points = [
  { id: 1, a: 0, b: 3 },
  { id: 2, a: 4, b: -1 },
  { id: 3, a: -1, b: 5 },
  { id: 4, a: 41, b: 2 },
  { id: 5, a: 69, b: 3 },
]

I want to iterate through each item and add a + b to get a new item d. I then want to add d within each object in the array to get a new value. When I try the below, it just adds 5 extra objects rather than appending the new element (key=value, ex: d: 3) to each individual object. What am I doing wrong here?

 points.forEach((item) => {
   var d = Math.abs(item.x) + Math.abs(item.y);
   console.log(d);
   points.item.push('d: ' + d);
 });

Your objects look to have a and b properties, not x and y properties? — CertainPerformance
– CertainPerformance, Commented Jun 15, 2018 at 2:50

Nikhil Aggarwal · Accepted Answer · 2018-06-15 02:48:41Z

3

Try following

var points = [{ id: 1, a: 0, b: 3 },{ id: 2, a: 4, b: -1 },{ id: 3, a: -1, b: 5 },{ id: 4, a: 41, b: 2 },{ id: 5, a: 69, b: 3 }];

points.forEach(o => o.d = Math.abs(o.a) + Math.abs(o.b));
console.log(points);

answered Jun 15, 2018 at 2:48

Nikhil Aggarwal

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Comments

hygull · Accepted Answer · 2018-06-15 03:45:30Z

1

@jcbridwe, you can use assign() method on Object to add missing property from source object to target object.

Please have a look at the below code.

Try the below code online at http://rextester.com/EPHYV10615.

var points = [
  { id: 1, a: 0, b: 3 },
  { id: 2, a: 4, b: -1 },
  { id: 3, a: -1, b: 5 },
  { id: 4, a: 41, b: 2 },
  { id: 5, a: 69, b: 3 },
]

for(var index in points){
    var a = points[index].a;
    var b = points[index].b;

    Object.assign(points[index], {d: a+b});
}

console.log(points);

» Output

[ { id: 1, a: 0, b: 3, d: 3 },
  { id: 2, a: 4, b: -1, d: 3 },
  { id: 3, a: -1, b: 5, d: 4 },
  { id: 4, a: 41, b: 2, d: 43 },
  { id: 5, a: 69, b: 3, d: 72 } ]

answered Jun 15, 2018 at 3:45

hygull

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2 Comments

gwydion93 Over a year ago

I went with this solution as it added the most relevance to changes I made to the code.

hygull Over a year ago

Thanks @gwydion93.

Leonid Pyrlia · Accepted Answer · 2018-06-15 11:16:57Z

0

Mutable approach:

points.forEach(o => o.d = o.a + o.b);

Immutable approach:

const newPoints = points.map(o => Object.assign({}, o, {d: o.a + o.b}))

answered Jun 15, 2018 at 11:16

Leonid Pyrlia

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