  <!DOCTYPE html> 
  <html> 
  <head> 
  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 
  <title>每天一個JavaScript實例-檢測表單數(shù)據(jù)</title> 
  <style> 
    [role="alert"]{ 
      background-color: #fcc; 
      font-weight: bold; 
      padding:5px; 
      border:1px dashed #000; 
    } 
    div{ 
      margin:10px 0; 
      padding:5px; 
      width:400px; 
      background-color: #fff; 
    } 
  </style> 
   
  <script> 
  window.onload = function(){ 
    document.getElementById("thirdfield").onchange = validateField; 
    document.getElementById("firstfield").onblur = mandatoryField; 
    document.getElementById("testform").onsubmit = finalCheck; 
  } 
  function validateField(){ 
    removeAlert(); 
    if(!isNaN(parseFloat(this.value))){ 
      resetField(this); 
    }else{ 
      badField(this); 
      generateAlert("You entered an invalid value in Third Field. only numeric values such as 105 or 3.45 are allowed"); 
    } 
  } 
  function removeAlert(){ 
    var msg = document.getElementById("msg"); 
    if(msg){ 
      document.body.removeChild(msg); 
    } 
  } 
  function resetField(elem){ 
    elem.parentNode.setAttribute("style","background-color:#fff"); 
    var valid = elem.getAttribute("aria-invalid"); 
    if(valid) elem.removeAttribute("aria-invalid"); 
  } 
  function badField(elem){ 
    elem.parentNode.setAttribute("style","background-color#fee"); 
    elem.setAttribute("aria-invalid","true"); 
  } 
  function generateAlert(txt){ 
    var txtNd = document.createTextNode(txt); 
    msg = document.createElement("div"); 
    msg.setAttribute("role","alert"); 
    msg.setAttribute("id","msg"); 
    msg.setAttribute("class","alert"); 
   
    msg.appendChild(txtNd); 
    document.body.appendChild(msg); 
  } 
   
  function mandatoryField(){ 
    removeAlert(); 
    if(this.value.length > 0 ){ 
      resetField(this); 
    }else{ 
      badField(this); 
      generateAlert("You must enter a value into First Field"); 
    } 
  } 
  function finalCheck(){ 
    //console.log("aaa"); 
    removeAlert(); 
   
    var fields =document.querySelectorAll('input[aria-invalid="true"]'); 
    //var fields =document.querySelectorAll("input[aria-invalid='true']");//錯誤?。?！ 
    console.log(fields); 
    if(fields.length > 0){ 
      generateAlert("You have incorrect fields entries that must be fixed before you can submit this form"); 
      return false; 
    } 
  } 
  </script> 
   
  </head> 
   
  <body> 
  <form id = "testform"> 
    <div> 
      <label for="firstfield">*first Field:</label><br /> 
      <input id="firstfield" name = "firstfield" type = "text" aria-required = "true" /> 
    </div> 
   
    <div> 
      <label for="secondfield">Second Field:</label><br /> 
      <input id="secondfield" name = "secondfield" type = "text" /> 
    </div> 
   
    <div> 
      <label for="thirdfield">Third Field(numeric):</label><br /> 
      <input id="thirdfield" name = "thirdfield" type = "text" /> 
    </div> 
   
    <div> 
      <label for="fourthfield">Fourth Field:</label><br /> 
      <input id="fourthfield" name = "fourthfield" type = "text" /> 
    </div> 
   
    <input type="submit" value = "Send Data" /> 
  </form> 
   
  </body> 
  </html>

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