Loop through all keys of multiple objects once?

Question

I have an array of object-names

['obj','obj2','objN']

These objects are nodes in an object

{
  obj: {
    key: value,
    key2: value,
  }
  obj2:{
    key3: value
  }
...
}

I know that i for one object I can do:

for (var key in obj) {
  if (obj.hasOwnProperty(key)) {
    console.log(key)
  }
}

but is it possible to loop through all keys of multiple objects without doing any duplicates?

Loop the Array, use the Array Keys and the Initial Object Property name. — Roko C. Buljan
– Roko C. Buljan, Commented Sep 25, 2015 at 20:40
If you just care about the keys only, regardless of what happens to the value, you could merge the objects together and then iterate through the keys of that one object. — BrockLee
– BrockLee, Commented Sep 25, 2015 at 20:40
It's your ?>{ and the property names are obj:, obj2 ... — Roko C. Buljan
– Roko C. Buljan, Commented Sep 25, 2015 at 20:41
You mean loop through the objects (node names are mentioned) paralelly or consecutively? The first one requires promises the latter requires a list containing your objects. — AndrasCsanyi
– AndrasCsanyi, Commented Sep 25, 2015 at 20:41

Will R. · Accepted Answer · 2015-09-25 21:35:46Z

Assuming a parent container object with the form:

var parentObj = 
{
    obj: {
        key: value,
        key2: value,
    }
    obj2: {
        key3: value
    }
    ...
}

Also if we want to include each sub-key only once, we have

var objNameArray = ['obj','obj2','objN'];
var allValues = [];
var usedKeys = {};

for(var i = 0; i < objNameArray.length; ++i){
    // If the parent object does not have a matching sub-object, skip to the
    // next iteration of the loop
    if(!parentObj[objNameArray[i]]) {
        continue;
    }
    var currentObj = parentObj[objNameArray[i]];
    var subKeys = Object.keys(currentObj);
    for(var j = 0; j < subKeys.length; ++j) {
        if(usedKeys[subKeys[j]]) {
            continue;
        }
        usedKeys[subKeys[j]] = true;
        allValues.push(currentObj[subKeys[j]]);
    }
}

All the values from all the keys in each sub-object will then be in the array allValues, and all the keys from each sub-object will be available by calling Object.keys(usedKeys);. Note that if sub-objects can also have sub-objects, this strategy needs to be adapted to support recursion.

guest271314 · Accepted Answer · 2015-09-25 21:06:05Z

0

If interpret Question correctly, try utilizing Object.keys()

var data = {
  obj: {
    key: 1,
    key2: 2,
  },
  obj2:{
    key3: 3
  }
};

for (var key in data) {
  console.log(Object.keys(data[key]))
}

answered Sep 25, 2015 at 21:06

guest271314

1

2 Comments

Himmators Over a year ago

won't this run the same keys multiple times if they exist in both obj and obj2?

guest271314 Over a year ago

@Himmators Is requirement to return only unique keys ?, or, if obj2 had key2 , do not return key2 it as part of result ? , as key2 previously iterated at obj ? What is expected result ?

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