Javascript-WeChat official account. The front-end initiates an ajax request to the background. why can't the backend get the sent value ??

Ecshop Background: Public Account front-end: {code...} back-end: {code...} There is always no value in this place. What is the problem ?? Ecshop Background:
Public Account front-end:

try{    function getData(method,path,searchStr,dataType,fn){      var xhr=new XMLHttpRequest();      method=method.toUpperCase();          xhr.open(method.toLowerCase(),(method==='POST') ? path : path+'?'+searchStr,true);          if (method==='POST'){            xhr.setRequestHeader('content-type','application/x-www-form-urlencoded');          }          xhr.send((method==='POST') ? searchStr : null);          xhr.onreadystatechange=function(){            if (this.readyState===4 && this.status===200){              var data=this.responseText;                           alert('fanyingshuju: '+data);            }          }    }    getData('GET','goods.php','act=price&id=' + goodsId + '&attr=' + attr + '&number=' + qty, changePriceResponse);      }catch(err){    alert('error: '+err);  }  

Background:

Die ('request initiated: '. $ _ REQUEST ['ac']);

There is always no value in this place. What is the problem ??

Reply content:

Ecshop Background:
Public Account front-end:

try{    function getData(method,path,searchStr,dataType,fn){      var xhr=new XMLHttpRequest();      method=method.toUpperCase();          xhr.open(method.toLowerCase(),(method==='POST') ? path : path+'?'+searchStr,true);          if (method==='POST'){            xhr.setRequestHeader('content-type','application/x-www-form-urlencoded');          }          xhr.send((method==='POST') ? searchStr : null);          xhr.onreadystatechange=function(){            if (this.readyState===4 && this.status===200){              var data=this.responseText;                           alert('fanyingshuju: '+data);            }          }    }    getData('GET','goods.php','act=price&id=' + goodsId + '&attr=' + attr + '&number=' + qty, changePriceResponse);      }catch(err){    alert('error: '+err);  }  

Background:

Die ('request initiated: '. $ _ REQUEST ['ac']);

There is always no value in this place. What is the problem ??

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