How can i find the total number of keys if the Object is inside an array

Question

Possible Duplicate:
How to efficiently count the number of keys/properties of an object in JavaScript?

var array = [{key:value,key:value}]

How can i find the total number of keys if it's an array of Object. When i do check the length of the array, it gives me one.

@Darin Dimitrov: Its an array of objects... not a plain object.. — John Cooper, Jul 17 '11 at 12:44
@Darin Dimitrov: His previous question is a dupe of that, this one asks something a little different. Not sure if it should've been a separate question, but I guess he didn't get responses from the earlier post. — BoltClock, Jul 17 '11 at 12:45
It is right - there is one object in the array. The question needs some polishing... Are you trying to get the total number of keys from the object in the array? Or something else? — Nicolae Albu, Jul 17 '11 at 12:46
@John Cooper, well then apply the technique in the dupe to `array[0]` which is a single object. — Darin Dimitrov, Jul 17 '11 at 12:46
@Nicolae Albu: Yes i am trying to get the total number of keys from the object in an array — John Cooper, Jul 17 '11 at 12:48

alex · Accepted Answer · 2011-07-17T13:02:25.257

2

If you want to know the number of unique properties of Objects in an Array, this should do it...

var uniqueProperties = [];

for (var i = 0, length = arr.length; i < length; i++) {
   for (var prop in arr[i]) {
       if (arr[i].hasOwnProperty(prop) 
           && uniqueProperties.indexOf(prop) === -1
          ) {
          uniqueProperties.push(prop);
       }
   } 
}

var uniquePropertiesLength = uniqueProperties.length;

jsFiddle.

Note that an Array's indexOf() doesn't have the best browser support. You can always augment the Array prototype (though for safety I'd make it part of a util object or similar).

edited Jul 17 '11 at 13:02

answered Jul 17 '11 at 12:43

alex

438,662
188
837
957

What does this mean uniqueProperties.indexOf(propertyName) === -1 – John Cooper Jul 17 '11 at 13:05
@JohnCooper: It checks to see if the property name already exists in the `uniqueProperties` `Array`. Be sure to check the footnote about browser compatibility. – alex Jul 17 '11 at 13:08

score 0 · Answer 2 · answered Jul 17 '11 at 12:44

0

If the array will only have one object, array[0] represents the object.

If there's more than one object, you'll need to decide what exactly you want to count.

answered Jul 17 '11 at 12:44

BoltClock

630,065
150
1,295
1,284

How can i find the total number of keys if the Object is inside an array

2 Answers2