Javascript: test if an object is an array.

**Tribo** · Mar 25th, 2008, 03:52 PM

Hi! I would like to know if there is an elegant way to test if an object is an array.

Example:

Code:

function ProcessObject(object) {
  //Test if it is an array.
  if(...) {
    for(int i=0; i < object.length; i++) {
      //object[i] ...
    }
  }
  else {
    //Don't process as an array.
    //object.value  ...
  }
}

In the code above, the function is receiving an object that could be an array or not. The main reason I want to know if it is an array is because I want to use the length property. Do anyone know if there is a property in DOM to know if an object is an array so I can invoke the length property without error?

Thanks a lot!

PS: I make it, in a not elegant way...

**mendhak** · Mar 25th, 2008, 04:55 PM

Code:

if(object.length != null)
{
//Array!
}

I think...

**Tribo** · Mar 25th, 2008, 07:48 PM

Originally Posted by mendhak

Code:

if(object.length != null)
{
//Array!
}

I think...

Perfect! It was so simple, and I was looking for a complicated solution...

Thanks a lot!!!

**mendhak** · Mar 26th, 2008, 04:02 AM

We can provide you with an overly complicated solution too, if that is what you wish.

**penagate** · Mar 26th, 2008, 07:52 PM

But strings have a length property, too. Are they arrays? Sort of, but probably not the type you mean.

Code:

if (object instanceof Array)
  // do something

**Tribo** · Mar 26th, 2008, 08:06 PM

Originally Posted by penagate

But strings have a length property, too. Are they arrays? Sort of, but probably not the type you mean.

Code:

if (object instanceof Array)
  // do something

I don't remember now, but I think that they are an array of DIVs, and with JavaScript I change the style so I can hide the information or not (it is a kind of Detail that the user could see and by default it isn't shown)

Regards!

**oceanebelle** · Mar 26th, 2008, 10:59 PM

This is brute but at least it does the job. Tested it too.

Code:

		if(obj[0] != null){
			alert("array of length " + obj.length);
		} else {
			alert("not an array");
		}

**penagate** · Mar 26th, 2008, 11:07 PM

What's wrong with instanceof? Does it smell funny or something?

**oceanebelle** · Mar 26th, 2008, 11:28 PM

Sorry, posting code for future reference on event listeners.

eace:

Code:

<html>
<head>
<title>Test Array</title>
<meta http-equiv="Content-Type" content="text/html; charset=shift_jis">
<script type="text/javascript">

	var mydivcount = 0;
	
	function checkIfArray(obj){	
	
		if(obj[0] != null){
			alert("array of length " + obj.length);
		} else {
			alert("not an array");
		}
	}	
	
	function addDiv(){	
		var newdiv = document.createElement('div');
		newdiv.setAttribute('id', 'mydiv');		
		newdiv.setAttribute('name', 'mydiv');						
		
                // dynamic event listener
		if (newdiv.addEventListener){
		  newdiv.addEventListener('click', removeDiv, false); 
		} else if (newdiv.attachEvent){
		  newdiv.attachEvent('onclick', removeDiv);
		}
		
		newdiv.appendChild(document.createTextNode("This is another div: " + (++mydivcount)))
		document.getElementById('addhere').appendChild(newdiv);
	}
	
	function removeDiv(evt){
		// target for Mozilla
		// srcElement for IE
		var el = (evt.target) ? evt.target : evt.srcElement;
		document.getElementById('addhere').removeChild(el);
	}

</script>
</head>

<body>
<div id="addhere" style="border:1 solid #000000; padding: 10px 0px 10px 0px ">
</div>

<input type="button" value="Add a DIV" onClick="addDiv()">
<input type="button" value="Check Array" onClick="checkIfArray(document.getElementsByName('mydiv'))">

</body>
</html>

**Tribo** · Mar 26th, 2008, 11:29 PM

Originally Posted by penagate

What's wrong with instanceof? Does it smell funny or something?

No, I think that it is the most elegant solution (it makes the code more legible). I'm going to try it.

Regards,

**oceanebelle** · Mar 26th, 2008, 11:32 PM

Originally Posted by penagate

What's wrong with instanceof? Does it smell funny or something?

I tried instanceof but if the collection is other than an Array type like divs for instance it won't detect it. the other testing is versatile enough I believe.

Code:

                if(obj instanceof Array){
			alert("array of length " + obj.length);
		} else {
			alert("not an array");
		}

**penagate** · Mar 26th, 2008, 11:49 PM

DOM node collections are not arrays. In fact there are 'live' collections as well as 'non-live' ones and fragments and so forth. None of these are derived from Array.

Thread: Javascript: test if an object is an array.

Thread Tools

Display

Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Re: Javascript: test if an object is an array.

Posting Permissions