null variable problem

I put a long script but the problem is small.

		var book1 = bobj1.value;
		var chapter1 = cobj1.value;
		var verse1 = vobj1.value;		
		var book2 = bobj2.value;
		var chapter2 = cobj2.value;
		var verse2 = vobj2.value;		

		var bcvQuotes = new Array();
		bcvQuotes[0] = "book1=";
		bcvQuotes[1] = "&chapter1=";
		bcvQuotes[2] = "&verse1=";
		bcvQuotes[3] = "&book2=";
		bcvQuotes[4] = "&chapter2=";
		bcvQuotes[5] = "&verse2=";	

		var bcv = new Array();
		bcv[0] = book1;
		bcv[1] = chapter1;
		bcv[2] = verse1;
		bcv[3] = book2;
		bcv[4] = chapter2;
		bcv[5] = verse2;		
		
		var urlExtension = document.getElementById('displayurl');
		var getKeyURL = "";
		//var getKeyURL = "book1="+book1+"&chapter1="+chapter1+"&verse1="+verse1+"&book2="+book2+"&chapter2="+chapter2+"&verse2="+verse2;
		urlExtension.innerHTML = "";
		//urlExtension.innerHTML = "book1="+book1+"&chapter1="+chapter1+"&verse1="+verse1+"&book2="+book2+"&chapter2="+chapter2+"&verse2="+verse2;

		for(a=0; a<bcv.length; a++){
			if(bcv[a]!= ""){
				getKeyURL += bcvQuotes[a] + bcv[a];
				urlExtension += bcvQuotes[a] + bcv[a];
			}
		}

Code (markup):

I don't know if this is written properly:
if(bcv[a]!= ""){

The reason this is happening is because the error shows:

 

It might be because cobj1 isn't point to any object. Recheck your text box (i suppose) id/name. Or try to use getElementById(). If this doesn't help, just post a full code.

 

Yeah you're right. I realized it after posting it. I'm using Ajax and the id wasn't parsed yet.
Here's the solved version:

function fillChapters1(){
	var req = createRequest();
	if(req){
		req.onreadystatechange = function(){
			var c = document.getElementById('showchapterdiv1');
			if(req.readyState){
				if(req.readyState == 4){
					if(req.status == 200){
						c.innerHTML = req.responseText;
					}
				}
			}
		}
			var divIds = new Array();
		divIds[0] = document.getElementById('showbookdiv1'); //not that it matters
		divIds[1] = document.getElementById('showchapterdiv1');
		divIds[2] = document.getElementById('showversediv1');
		divIds[3] = document.getElementById('showbookdiv2');
		divIds[4] = document.getElementById('showchapterdiv2');
		divIds[5] = document.getElementById('showversediv2');
		
		var urlExtension = document.getElementById('displayurl');
		
//		var getKeyURL = "book1="+book1+"&chapter1="+chapter1+"&verse1="+verse1+"&book2="+book2+"&chapter2="+chapter2+"&verse2="+verse2;
//		urlExtension.innerHTML = "book1="+book1+"&chapter1="+chapter1+"&verse1="+verse1+"&book2="+book2+"&chapter2="+chapter2+"&verse2="+verse2;
		
		urlExtension.innerHTML = "";
		var getKeyURL = "";
		
		var bcv = new Array();
		var bcvQuotes = new Array();
		
		if(divIds[0].innerHTML!= 0){
			bcvQuotes[0] = "book1=";
			var bobj1 = document.getElementById('selbook1');
			bcv[0] = bobj1.value;
			urlExtension.innerHTML += bcvQuotes[0]+bcv[0];
			getKeyURL += bcvQuotes[0]+bcv[0];
			for(a=0; a<6; a++){
				if(document.getElementById('txtarea_'+[a]).value!= ""){
					getKeyURL += "&txtarea" + [a] + "=";
					urlExtension.innerHTML += "&txtarea" + [a] + "=";
				}
				getKeyURL += document.getElementById('txtarea_'+[a]).value;
				urlExtension.innerHTML += document.getElementById('txtarea_'+[a]).value;
			}
		}
		if(divIds[1].innerHTML!= 0){
			bcvQuotes[1] = "&chapter1=";
			var cobj1 = document.getElementById('selchapter1');
			bcv[1] = cobj1.value;
			urlExtension.innerHTML += bcvQuotes[1]+bcv[1];
			getKeyURL += bcvQuotes[1]+bcv[1];
		}
		if(divIds[2].innerHTML!= 0){
			bcvQuotes[2] = "&verse1=";
			var vobj1 = document.getElementById('selverse1');
			bcv[2] = vobj1.value;
			urlExtension.innerHTML += bcvQuotes[2]+bcv[2];
			getKeyURL += bcvQuotes[2]+bcv[2];
		}
		if(divIds[3].innerHTML!= 0){
			bcvQuotes[3] = "&book2=";
			var bobj2 = document.getElementById('selbook2');
			bcv[3] = bobj2.value;
			urlExtension.innerHTML += bcvQuotes[3]+bcv[3];
			getKeyURL += bcvQuotes[3]+bcv[3];
		}
		if(divIds[4].innerHTML!= 0){
			bcvQuotes[4] = "&chapter2=";
			var cobj2 = document.getElementById('selchapter2');
			bcv[4] = cobj2.value;
			urlExtension.innerHTML += bcvQuotes[4]+bcv[4];
			getKeyURL += bcvQuotes[4]+bcv[4];
		}
		if(divIds[5].innerHTML!= 0){
			bcvQuotes[5] = "&verse2=";
			var vobj2 = document.getElementById('selverse2');
			bcv[5] = vobj2.value;
			urlExtension.innerHTML += bcvQuotes[5]+bcv[5];
			getKeyURL += bcvQuotes[5]+bcv[5];
		}
	req.open("GET","getChapters1.php?"+getKeyURL,true);
	req.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
	req.send(null);
	}
}

Code (markup):

But I wonder if it would be possible to shrink this code with a for loop? It works as it is but the js page has this times 6, meaning in 6 functions.