js中判断变量是否为数字 isNaN函数

document.write(isNaN(123));//false
document.write(isNaN(-1.23));//false
document.write(isNaN(5-2));//false
document.write(isNaN(0));//false
document.write(isNaN("Hello"));//true
document.write(isNaN("2005/12/12"));//true
document.write(isNaN("6/2"));//true
document.write(isNaN("3"));//false

if(isNaN(document.login.imgcode.value)){
   alert('验证码必须是数字！')
   document.login.imgcode.focus();
   return false;
}

if(!isNum(document.getElementById("prjSum").value)){
    alert("造价只能是数字");
    document.getElementById("prjSum").focus();
    return false;
   
    }