以下代码，可以完成input、radio、checkbox、textarea等的必填属性检测。

在网页中经常需要限制某些表单项是必填项，此时就需要借助js脚本来检测。

代码：

<script language="javascript"> //检查必填字段 //(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; } }; }; </script>