通用的校验必填项不能为空(包括input框，单选框，复选框,文本域)

   通用的校验必填项不能为空(包括input框，单选框，复选框,文本域)

 

//检查必填字段
//(通用的校验必填项不能为空(包括input框，单选框，复选框,文本域))
var elem = document.getElementById("age");
function checkRequired(elem){
		var name = elem.name;
		if(elem.type == "checkbox" || elem.type == "radio"){
			var results=[];
			results.numChecked = 0;
			var input = document.getElementsByTagName("input");
			for(var i=0;i<input.length;i++){
				if(input[i].name == name){
					results.push(input[i]);
					if(input[i].checked){
						results.numChecked++;
					}
				}
			}
			return results.numChecked;
		
		}else{ 
			return elem.value.length > 0 && elem.value != elem.defaultValue;
		}
	}

//-----------------------------------------------------
//检查输入元素是否键入了信息的通用函数
function checkRequired(elem){
	if(elem.type == "checkbox" || elem.type == "radio")
		return getInputsByName(elem.name).numChecked;
	else 
		return elem.value.length > 0 && elem.value != elem.defaultValue;
}
//找出指定name的所有input元素（对查找 以及处理复选框或单选框十分有用）
function getInputsByName(name){
	var results=[];
	results.numChecked = 0;
	var input = document.getElementsByTagName("input");
	for(var i=0;i<input.length;i++){
		if(input[i].name == name){
			results.push(input[i]);
			if(input[i].checked){
				results.numChecked++;
			}
		}
	}
	return results;
}

window.onload = function(){
	document.getElementsByTagName("form")[0].onsubmit=function(){
		var elem = document.getElementById("age");
		if(!checkRequired(elem)){
			alert("Required field is empty "+"you must be over 13 to use this site.");
			return false;
		}
		var elem = document.getElementById("name");
		if(!checkRequired(elem)){
			alert("Required field is empty - please provide ");
			return false;
		}
	};
};