js创建验证码

    <script>
        window.onload=function(){
            var code=document.getElementById("code");
            var code_text='';
            createCode();
            code.onclick=function(){
                
                createCode();
            }
            
            function createCode(){//创建验证码
                code_text="";
            var datas=['Q','W','E','R','T','Y','U','I','O','P',
            'A','S','D','F','G','H','J','K','L','M','N','B','V','C','X','Z',];
            for(var i=0 ;i<4;i++){
                
             var index=Math.floor(Math.random()*datas.length);
                 code_text +=datas[index];
            }
            code.innerHTML=code_text;    
        }
    }
        
    </script>