<form action="" id="myform" oninput="num.value=http://www.mamicode.com/parseInt(num1.value)+parseInt(num2.value)">
        <input type="number" id="num1">+
        <input type="number" id="num2">=
        <output name="num" for="num1 num2"></output>            
    </form>

html5，output标签应用举例