2015.7.9js-06 命名的规范（参考类型）

window.onload = function(){
    var oText1 = document.getElementById("text1");
    var oText2 = document.getElementById("text2");
    var obtn = document.getElementById("btn");

    obtn.onclick = function(){
        var num1 = parseInt(oText1.value);
        var num2 = parseInt(oText2.value);

        if(isNaN(num1)){
            alert("you enter the number is error");
        }else if(isNaN(num2)){
            alert("you enter the number is error");
        }else{
            alert(num1 + num2);
        }
    }
}