Add together all objects in an array of objects

Question

I have an array of objects that looks like the next example:

let tryout = [
  {text: 1, video: 1, photo: 2, song: 1},
  {text: 2, video: 3, photo: 1},
  {text: 4, video: 2, photo: 2},
]

And I want to add them to get this kind of object at the end:

let newObjet = {
  text: 7,
  video: 6,
  photo: 5,
  song: 1
}

What would be the best way to do this. I am trying with reduce() but all I am getting is a merging of objects keys, and the values are not adding up.

One important thing is that I don't know what keys are gonna be inside of objects.

This is my attempt (not working as expected):

var resultObject = tryout.reduce(function(result, currentObject)
{
    for (var key in currentObject)
    {
        if (currentObject.hasOwnProperty(key)) {
            result[key] = currentObject[key];
        }
    }

    return result;
}, {});

If it doesn't work, include a minimal reproducible example of your best effort. — Emile Bergeron
– Emile Bergeron, Commented May 21, 2019 at 20:55
You should show the code you tried so we can show you where you are having trouble. This is definitely a case for reduce though. — GifCo
– GifCo, Commented May 21, 2019 at 20:56
I added my attempt. I don't really like a code on that Sum values of objects array because I dont know what keys I am gonna have in objects — Igor-Vuk
– Igor-Vuk, Commented May 21, 2019 at 21:00

Shidersz · Accepted Answer · 2019-05-21 21:21:43Z

One solution is to use Array.reduce() in combination with Object.entries()

let tryout = [
  {text: 1, video: 1, photo: 2, song: 1},
  {text: 2, video: 3, photo: 1},
  {text: 4, video: 2, photo: 2}
]

let res = tryout.reduce((acc, obj) =>
{
    Object.entries(obj).forEach(([k, v]) =>
    {
        acc[k] = (acc[k] || 0) + v;
    });

    return acc;
}, {});

console.log(res);

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

In relation to your code, you have an issue on the if sentence, instead of checking next condition:

if (currentObject.hasOwnProperty(key)) {...}

That will be true every time, the way you are using it (inside a loop that traverses the same object), you need to check if result.hasOwnProperty(key) in order to decide if adds the number to the previous stored result for that key or to assign it to the key.

let tryout = [
  {text: 1, video: 1, photo: 2, song: 1},
  {text: 2, video: 3, photo: 1},
  {text: 4, video: 2, photo: 2}
]

var resultObject = tryout.reduce(function(result, currentObject)
{
    for (var key in currentObject)
    {
        if (result.hasOwnProperty(key))
            result[key] += currentObject[key];
        else
            result[key] = currentObject[key];
    }

    return result;
}, {});

console.log(resultObject);

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

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