JavaScript - How To Return A True Or False Value From A Function To Disable Automatic Postback

<input type="image" name="ctl00${cut}" tabindex="-1" title="Click to look up the details" src="images/load_details.png" onclick="LoadDetails(); return false;" style="border-width:0px;" />

<script type="text/javascript">

function changeColor(color) {
document.getElementById("nav").style.borderColor = color;
}

</script>

<a href="index.php" onclick="changeColor('red') ;return false">HOME</a>
<a href="about.php" onclick="changeColor('blue') ;return false">ABOUT</a>
<a href="contact.php" onclick="changeColor('orange') ;return false">CONTACT</a>

function checkSCItems() { //check sccost not blank due to ajax need to do lookup
	xmlHttp=GetXmlHttpObject()
	if (xmlHttp==null) {
		alert ("Browser does not support HTTP Request");
		return;
	}

	var params = "?scnumber=" + escape(document.getElementById('scnumber').value);
	var url="_check_scitems.php";
	url=url+params;
	ajaxedInner = "";
	xmlHttp.open("GET",url,true);
	xmlHttp.setRequestHeader("If-Modified-Since", "Fri, 31 Dec 1999 23:59:59 GMT");
	xmlHttp.onreadystatechange=stateChanged;
	xmlHttp.send(null);
	xmlHttp.onreadystatechange = function() {
		if (xmlHttp.readyState == 4){
			if (xmlHttp.status == 200) {
				var checkSCItemsResponse = xmlHttp.responseText;
				if(checkSCItemsResponse == 'found') {
					return true;
				} else {
					window.location.hash = 'scpricebuildup2';
					alert('You must first create some cost items');
					return false;
				}
			} else {
				alert('There was a problem, please try again, or contact the Administrator');
				return false;
			}
		}
	}
}

<a href='javascript:;' onclick="if(checkSCItems() && validateText(document.subcontract_order,['scdate','scworks','scpayment','scfirstpayment','scpaymentinterim','scbalance','scretentionat','sccommence','sccompletion','sclabour','scplant','scmaterials']) && validateDate(document.subcontract_order, ['scdate','scfirstpayment','scbalance','sccommence','sccompletion']) && validateSelectNoBlank(document.subcontract_order, ['trading_name'])){window.open('subcontract_order_print.php?id=<?php echo writeIfSet($id) ?>')}">

<SCRIPT type="text/javascript">
	function validateForm() {
		if (document.forms["form"]["quantity"].value== (+$row['quantity']) {
			alert ("Cannot submit because the quantity specified is not available.");
			return false;
		}
	}
</SCRIPT>
<INPUT name="quantity" onsubmit="return validateForm()>

//Last Updated 5/10/12

/*Regex list of on-site domains, pipe and backslash delimited. */
var wa_onsiteDomains = /mydomain\.com|my2nddomain\.com|my3rddomain\.com|javascript/i;

/*Used to unobtrusivly add events to objects*/
function unobtrusiveAddEvent (element,event,fn) {
   var old = (element[event]) ? element[event] : function () {};
   element[event] = function () {fn(); old();};
}

function wa_crossDomainLink(i) {
	return function () { 
		var thisLink = decodeURI(wa_links[i]);
		var thisLinkTarget = wa_links[i].target;
		if (typeof(_gaq) == "object") {
			if(thisLinkTarget == "_blank") {
				var wa_myTracker=_gat._getTrackerByName();
				var wa_fullUrl = wa_myTracker._getLinkerUrl(thisLink);
				window.open(wa_fullUrl); return false;
			} else {
				_gaq.push(['_link', thisLink]); return false;
			}
		}
	};
}

var wa_links = document.links;
if ( wa_links ){
	for(var i=0; i<wa_links.length; i++) {
		if( wa_links[i].href.match(wa_onsiteDomains) && !wa_links[i].href.match(location.hostname)){
			unobtrusiveAddEvent( wa_links[i], 'onclick' , wa_crossDomainLink(i));
		}
	}
}

      <script type="text/javascript">
    //FIRST FUNCTION FOR FORMS[0]
    function signinForm(){
    
    		// var sameWarning = "The required fields were not submitted for the following error(s).  \n \n";
    		var warningLogin = "The following field(s) require an entry: \n \n";
    		var sameWarning = warningLogin;
    		
    		var userName = document.forms[0].userName.value;
    		var pswd = document.forms[0].pswd.value;
    		
    		if(userName == ""){ 
    		sameWarning += " - First Name \n";
    		}
    		
    		if(pswd == ""){ 
    		sameWarning += " - Password \n";
    		}
    
    		if (warningLogin == sameWarning){ 
    			return true; 
    			}
    		
    		else  { 
    			window.alert(sameWarning); 	
    		}
        return false;	
       }
     
  //SECOND FUNCTION CALL FOR FORMS[1] 
    function saveSignUp(){
    
    		// var warning = "The required fields were not submitted for the following error(s).  \n \n";
    		var warning = "The following field(s) require an entry: \n \n";
    		var same = warning;
    		
    		var firstName = document.forms[1].firstName.value;
    		var lastName = document.forms[1].lastName.value;
    		var email = document.forms[1].email.value;
    		var phone = document.forms[1].phoneNumber.value;
    		
    		if(firstName == ""){ 
    		//firstName.style.backgroundColor="red";
    		warning += " - First Name \n";
    		}
    		
    		if(lastName == ""){ 
    		warning += " - Last Name \n";
    		}
    
    		if(email == ""){ 
    		warning += " - Email \n";
    		}
    
    		if(phone == ""){ 
    		warning += " - Work Phone \n";
    		}
    		
    		if(phone < 5 ){
    			warning += " - Must be a numberssss \n";
    			}
    
    		if (warning == same){
    			return true; 
    		} 
    		
    		else  { 
    			alert(warning); 		
    		}
    	return false;
       }
       
    </script>

    <h1>Login</h1>
    <form method="post" onsubmit="return signinForm();" action="" >
        <input type="text" placeholder="Username/Email" name="userName">
        <input type="password" placeholder="Password" name="pswd" id="pswd">
        <input type="submit" onclick="signinForm();" value="Sign In">
    </form>
    <h1>Sign Up!</h1>
        <form method="post" onsubmit="return saveSignUp()" action="" >
        <input type="text" placeholder="First Name" name="firstName">
        <input type="text" placeholder="Last Name" name="lastName">
        <input type="text" placeholder="Email" name="email">
        <input type="text" placeholder="Phone Number" name="phoneNumber">
        <input type="submit" onclick="saveSignUp();" class="button wide" value="Request an Account">		
</form>

<script type="text/javascript">
  function disable(element)
  {
    var input = document.getElementById(element).getElementsByTagName("input");
    for(var i = 0; i < input.length; i++)
    {
      input[i].setAttribute("disabled","true");
    }
  }
</script>

<script type="text/javascript">
  function enable(element)
  {
    var input = document.getElementById(element).getElementsByTagName("input");
    for(var i = 0; i < input.length; i++)
    {
      input[i].setAttribute("disabled","false");
    }
  }
</script>

<form>
  <input type="radio" name="test" onclick="disable('D1')" /> disable<br/>
  <input type="radio" name="test" onclick="enable('D1')" /> enable<br/>
  <fieldset id="D1">
    <input class="" type="text" value="test value1" /><input class="" type="text" value="test value2" /><br/>
    <input class="" type="text" value="test value3" /><input class="" type="text" value="test value4" /><br/>
    <input class="" type="text" value="test value5" /><input class="" type="text" value="test value6" /><br/>
  </fieldset>
</form>

<form>
  <input type="radio" name="test" onclick="disable('D1')" />
  <fieldset id="D1">
    <input class="" type="text" value="test value1" /><input class="" type="text" value="test value2" />
  </fieldset>
  <input type="radio" name="test" onclick="disable('D2')" />
  <fieldset id="D2">
    <input class="" type="text" value="test value3" /><input class="" type="text" value="test value4" />
  </fieldset>
  <input type="radio" name="test" onclick="disable('D3')" />
  <fieldset id="D3">
    <input class="" type="text" value="test value5" /><input class="" type="text" value="test value6" />
  </fieldset>
</form>

function codeAddress() {
    var address = document.getElementById("address").value;
    geocoder.geocode( { 'address': address}, function(results, status) {
      if (status == google.maps.GeocoderStatus.OK) {
        map.setCenter(results[0].geometry.location);
		map.setZoom(10);
      } else {
        alert("City was not found: " + status);
      }
    });
  }

function centerAndZoom(line) {
  bounds = line.getBounds();
  map.setCenter(bounds.getCenter(map), map.getBoundsZoomLevel(bounds));
}