一个检测表单数据的JavaScript实例

        《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("p");   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']");//错误！！！   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》       
   
     *first Field:
        
     
     Second Field:
        
     
     Third Field(numeric):
        
     
     Fourth Field:
        
      
    

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