<script>
function yzm(){
var arr = ['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','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','0','1','2','3','4','5','6','7','8','9'];
var str = '';
for(var i = 0 ; i < 4 ; i ++ )
str += ''+arr[Math.floor(Math.random() * arr.length)];
return str;
}
</script>
<button onclick="document.getElementById('yzm').innerHTML = yzm();">重获验证码</button>
<div id="yzm"></div>
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