Onclick javascript-Updating a record

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/30.0/apex.js")}

try{
	var caseId = '{!Case.id}';	
	if(confirm('Are you sure you want to assign this case to yourself.')) {
		//fetch logged in User details
		var user = sforce.connection.getUserInfo();
		var CaseToUpdate = []; 
		var rec =sforce.connection.query("Select id,ownerId from Case where id='"+caseId+"' Limit 1"); 
		var records = rec.getArray("records");
		if(records.length) { 
			for(var j=0;j<records.length;j++){ 
				var cas = new sforce.SObject("Case");
				cas.Id=records[j].Id;
				cas.ownerId=user.userId; 
				//here modify any field value
				CaseToUpdate.push(cas);
			}
			result = sforce.connection.update(CaseToUpdate);
			if (result[0].success == 'true'){
				alert('Case assigned successfully');
				window.location.href = '/'+caseId;
			}else{
				alert('An error has occoured. Error: '+result[0].errors.message);
				window.location.href = '/'+caseId ;
			}
		}
	}
}catch(e){
	alert('some system error occured. Please try later');
}