<script language="javascript">
var code; //在全局 定義驗(yàn)證碼
function createCode()
{ //創(chuàng)建驗(yàn)證碼函數(shù)
 code = "";
 var codeLength =4;//驗(yàn)證碼的長度
 var selectChar = new Array(0,1,2,3,4,5,6,7,8,9,'a','b','c','d','e','f','g','h','i','j','k',
  'l','m','n','o','p','q','r','s','t','u','v','w','x','y','z');//所有候選組成驗(yàn)證碼的字符，當(dāng)然也可以用中文的
 for(var i=0;i<codeLength;i++)
 { 
 var charIndex =Math.floor(Math.random()*36);
 code +=selectChar[charIndex]; 
 }
// 設(shè)置驗(yàn)證碼的顯示樣式，并顯示
 document.getElementById("discode").style.fontFamily="Fixedsys"; //設(shè)置字體
 document.getElementById("discode").style.letterSpacing="5px"; //字體間距
 document.getElementById("discode").style.color="#0ab000"; //字體顏色
 document.getElementById("discode").innerHTML=code; // 顯示
}
function but()
{//驗(yàn)證驗(yàn)證碼輸入是否正確
 var val1=document.getElementById("t1").value;
 var val2=code;
 if(val1!=val2){
  alert("驗(yàn)證碼錯(cuò)誤!");
 document.getElementById('t1').value="";
  }
 }
</script>

 <div class="input">
    <input id="t1" type="text" name="u" placeholder="驗(yàn)證碼" onblur="but()" />
    <span id="discode"></span>
    <input type="button" value="換一換" class="c" style="height:20px;"onClick="createCode()">
    </div>