<!DOCTYPE html>
<html>
    <head>
        <meta charset=utf-8>
    </head>
    <body>
            
    	<input id="input" type="text" onchange="changespan()"/>
        <span id="span"></span>

        <script type="text/javascript">
            // 补全代码  实时用oninput
            function changespan(){
                span.innerText = input.value;
            }
            
        </script>
    </body>
</html>