Creating deep-nested objects in Javascript

Question

When loading JSON from a server, I need to create objects. The objects do not always exist beforehand.Therefore I have to check that each level exists before adding a new level. Is there a better way to do this, then the following way:

var talkerId = commentDB.val().to;
var commentId = commentDB.val().id

if (!store.talkers.hasOwnProperty(talkerId)) {
    store.talkers[talkerId] = {}
}
if (!store.talkers[talkerId].hasOwnProperty(comments)) {
    store.talkers[talkerId] = { comments: {} };
}
if (!store.talkers[talkerId].comments.hasOwnProperty(commentId)) {
    store.talkers[talkerId].comments[commentId] = {}
}
store.talkers[talkerId].comments[commentId].author = commentDB.val().author;

Could you not simply return JSON from the server and then use JSON.parse() to convert to an object? — Reinstate Monica Cellio
– Reinstate Monica Cellio, Commented Mar 26, 2018 at 12:01
I can't return from the server, because I join two fields of data, and create combined JSON in the client. — Tal Yaron
– Tal Yaron, Commented Mar 26, 2018 at 12:14
So you make 2 calls to the server, each of them making a DB call, then you return 2 datasets to the client and that merges them into one object? — Reinstate Monica Cellio
– Reinstate Monica Cellio, Commented Mar 26, 2018 at 12:18

Nina Scholz · Accepted Answer · 2018-03-27 06:24:54Z

2

You cour reduce the keys by using the object an check if the key exist. if not create a new property with an empty object.

var dbValue = commentDB.val();

[dbValue.to, 'comments', dbValue.id].reduce(
    (o, k) => o[k] = o[k] || {},
    store.talkers
).author = commentDB.val().author;

edited Mar 27, 2018 at 6:24

answered Mar 26, 2018 at 12:03

Nina Scholz

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1 Comment

Tal Yaron Over a year ago

Thanks, very cool, but reduce has logic that I find hard to follow when maintaing a code

Kiran Shinde · Accepted Answer · 2018-03-26 12:05:27Z

1

Why don't you create a function

function checkAndCreateProperty(arr, baseVar) {
   for(var i = 0; i < arr.length; i++) {
       if (!baseVar.hasOwnProperty(arr[i])) {
           baseVar[arr[i]] = {};
      }
      baseVar = baseVar[arr[i]];
   }
}


checkAndCreateProperty(["talkerId", "comments", commentDB.val().id, commentDB.val().author], store.talkers)

answered Mar 26, 2018 at 12:05

Kiran Shinde

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Comments

Tal Yaron · Accepted Answer · 2018-03-26 12:31:18Z

1

After the suggestion of @31piy I went for the most simple solution:

using lodash _.set

var talkerId = commentDB.val().to;
var commentId = commentDB.val().id;

_.set(store.talkers, '[' + talkerId + '].comments[' + commentId + '].author', commentDB.val().author)

answered Mar 26, 2018 at 12:31

Tal Yaron

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