Finding the number of keys in an object

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

var values = [{
    'SPO2': 222.00000,
    'VitalGroupID': 1152,
    'Temperature': 36.6666666666667,
    'DateTimeTaken': '/Date(1301494335000-0400)/',
    'UserID': 1,
    'Height': 182.88,
    'UserName': null,
    'BloodPressureDiastolic': 80,
    'Weight': 100909.090909091,
    'TemperatureMethod': 'Oral',
    'Resprate': null,
    'HeartRate': 111,
    'BloodPressurePosition': 'Standing',
    'VitalSite': 'Popliteal',
    'VitalID': 1135,
    'Laterality': 'Right',
    'HeartRateRegularity': 'Regular',
    'HeadCircumference': '',
    'BloodPressureSystolic': 120,
    'CuffSize': 'XL'
}];

for (i=0; i < values.length; i++) {
        alert(values.length) // gives me 2.

How can find how many keys my object has?

Two things: 1) Why are you looping through `values.length` yet also alerting `values.length`? 2) I swear `values.length` is not going to give you 2. — BoltClock, Jul 17 '11 at 11:49
http://stackoverflow.com/questions/5223/length-of-javascript-associative-array — felix, Jul 17 '11 at 11:50
Further to @BoltClock's comment, [`alert(values.length);` gives: `1`](http://jsfiddle.net/davidThomas/UvthC/). And, incidentally, from my own training, the saturated partial arterial pressure of oxygen (`SPO2`), should be a percentage value of up to `100` (percent, obviously). Where's the `222.00000` coming from? I'm not intending to be confrontational, but I **am** curious... =) — David says reinstate Monica, Jul 17 '11 at 11:51

score 69 · Accepted Answer · answered Jul 17 '11 at 11:50

var value = {
    'SPO2': 222.00000,
    'VitalGroupID': 1152,
    'Temperature': 36.6666666666667,
    'DateTimeTaken': '/Date(1301494335000-0400)/',
    'UserID': 1,
    'Height': 182.88,
    'UserName': null,
    'BloodPressureDiastolic': 80,
    'Weight': 100909.090909091,
    'TemperatureMethod': 'Oral',
    'Resprate': null,
    'HeartRate': 111,
    'BloodPressurePosition': 'Standing',
    'VitalSite': 'Popliteal',
    'VitalID': 1135,
    'Laterality': 'Right',
    'HeartRateRegularity': 'Regular',
    'HeadCircumference': '',
    'BloodPressureSystolic': 120,
    'CuffSize': 'XL'
};

alert(Object.keys(value).length);

How can i find the total number of keys if the Object is inside an array — John Cooper, Jul 17 '11 at 12:40

beardhatcode · Answer 2 · 2011-07-17T11:55:38.423

5

try

Object.keys(values).length

see: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/keys

for compatiblity

if(!Object.keys) Object.keys = function(o){
 if (o !== Object(o))
      throw new TypeError('Object.keys called on non-object');
 var ret=[],p;
 for(p in o) if(Object.prototype.hasOwnProperty.call(o,p)) ret.push(p);
 return ret;
}

or use:

function numKeys(o){
var i=0;
for(p in o) if(Object.prototype.hasOwnProperty.call(o,p)){ i++};
return i;
}

edited Jul 17 '11 at 11:55

answered Jul 17 '11 at 11:49

beardhatcode

3,895
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2

which you should attribute to its source... – Alnitak Jul 17 '11 at 11:55

phihag · Answer 3 · 2011-07-17T12:08:33.997

5

function numKeys(o) {
   var res = 0;
   for (var k in o) {
       if (o.hasOwnProperty(k)) res++;
   }
   return res;
}

or, in newer browsers:

function numKeys(o) {
   return Object.keys(o).length;
}

In your example, values is an array with one element, so you'd call numKeys(values[0]) to find out.

edited Jul 17 '11 at 12:08

answered Jul 17 '11 at 11:49

phihag

245,801
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#2 should be `Object.keys(o).length` – Alnitak Jul 17 '11 at 11:57

pimvdb · Answer 4 · 2011-07-17T11:55:19.033

-2

You can iterate and just count:

var i = 0;
for(var key in values[0]) if(values[0].hasOwnProperty(key)) i++;
// now i is amount

edited Jul 17 '11 at 11:55

answered Jul 17 '11 at 11:48

pimvdb

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This will include properties defined by the object prototype – phihag Jul 17 '11 at 11:52
@phihag: You're correct but you should not extend `Object.prototype` anyway. – pimvdb Jul 17 '11 at 11:53
1

@pimvdb indeed you shouldn't, but you should program defensively in case one of the libraries you're using has. – Alnitak Jul 17 '11 at 11:54

Finding the number of keys in an object

4 Answers4