[javascript] How do I count a JavaScript object's attributes?

Suppose I have the following object in JavaScript:

var object = {
  "key1": "value1",
  "key2": "value2",
  "key3": "value3"
}; 

How do I find out how many values exist in the object?

You can do that by using this simple code:

Object.keys(myObject).length

This function makes use of Mozilla's __count__ property if it is available as it is faster than iterating over every property.

function countProperties(obj) {
  var count = "__count__",
  hasOwnProp = Object.prototype.hasOwnProperty;

  if (typeof obj[count] === "number" && !hasOwnProp.call(obj, count)) {
    return obj[count];
  }
  count = 0;
  for (var prop in obj) {
    if (hasOwnProp.call(obj, prop)) {
      count++;
    }
  }
  return count;
};

countProperties({
  "1": 2,
  "3": 4,
  "5": 6
}) === 3;

For those which will read this question/answers, here is a JavaScript implementation of Dictionary collection very similar as functionality as .NET one: JavaScript Dictionary

 var miobj = [
  {"padreid":"0", "sw":"0", "dtip":"UNO", "datos":[]},
  {"padreid":"1", "sw":"0", "dtip":"DOS", "datos":[]}
 ];
 alert(miobj.length) //=== 2

but

 alert(miobj[0].length) //=== undefined

this function is very good

Object.prototype.count = function () {
    var count = 0;
    for(var prop in this) {
        if(this.hasOwnProperty(prop))
            count = count + 1;
    }
    return count;
}

alert(miobj.count()) // === 2
alert(miobj[0].count()) // === 4

Although it wouldn't be a "true object", you could always do something like this:

var foo = [
  {Key1: "key1"},
  {Key2: "key2"},
  {Key3: "key3"}
];

alert(foo.length); // === 3

You can iterate over the object to get the keys or values:

function numKeys(obj)
{
    var count = 0;
    for(var prop in obj)
    {
        count++;
    }
    return count;
}

It looks like a "spelling mistake" but just want to point out that your example is invalid syntax, should be

var object = {"key1":"value1","key2":"value2","key3":"value3"};

Use underscore library, very useful: _.keys(obj).length.

EDIT: this will case errors with jquery to happen, plus some other inconveniences. YOU SHOULD NOT USE IT: (perhaps if one could add a privaate method instead of a public property function, this would be OK, but don't have the time now). Community wikied

do not use:

Even though javascript's object by default doesn't have the count function, classes are easily extendable, and one can add it oneself:

Object.prototype.count = function () {
    var count = 0;
    for(var prop in this) {
        if(this.hasOwnProperty(prop))
            count = count + 1;
    }
    return count;
}

So that after that one can execute

var object = {'key1': 'val1', 'key2':'val2', 'key3':'val3'};
console.log(object.count()); // 3

As a conclusion, if you want count functionality in objects, you need to copy the code from code block 1, and paste it early in execution time ( before you call the count ).

Let me know if that works for you!

Regards, Pedro