wx.request({
    url: 'https://www.yourhost.com/weixin/WeiActivity/payJoinfee',//改成你自己的链接
    header: {
      'Content-Type': 'application/x-www-form-urlencoded'
    },
    method:'POST',
    success: function(res) {
      console.log(res.data);
      console.log('调起支付');
      wx.requestPayment({
        'timeStamp': res.data.timeStamp,
        'nonceStr': res.data.nonceStr,
        'package': res.data.package,
        'signType': 'MD5',
        'paySign': res.data.paySign,
        'success':function(res){
          console.log('success');
          wx.showToast({
            title: '支付成功',
            icon: 'success',
            duration: 3000
          });
        },
        'fail':function(res){
          console.log('fail');
        },
        'complete':function(res){
          console.log('complete');
        }
      });
    },
    fail:function(res){
      console.log(res.data)
    }
  });

//支付费用
 public function payJoinfee(){
 $appid='wx888888888';
 $openid='oCQwY0Q_pzrQpu8888888';
 $mch_id='141388888';
 $key='9A0A86888888888';
 
 import('Weixin.Lib.WeixinPay');
 $weixinpay = new \WeixinPay($appid,$openid,$mch_id,$key);
 $return=$weixinpay->pay();

 $this->response($return,'json');
 }

<"abcdefghijklmnopqrstuvwxyz0123456789"; 
 $str ="";
 for ( $i = 0; $i < $length; $i++ ) { 
  $str.= substr($chars, mt_rand(0, strlen($chars)-1), 1); 
 } 
 return $str;
 }
 //作用：生成签名
 private function getSign($Obj){
 foreach ($Obj as $k => $v){
  $Parameters[$k] = $v;
 }
 //签名步骤一：按字典序排序参数
 ksort($Parameters);
 $String = $this->formatBizQueryParaMap($Parameters, false);
 //签名步骤二：在string后加入KEY
 $String = $String."&key=".$this->key;
 //签名步骤三：MD5加密
 $String = md5($String);
 //签名步骤四：所有字符转为大写
 $result_ = strtoupper($String);
 return $result_;
 }
 ///作用：格式化参数，签名过程需要使用
 private function formatBizQueryParaMap($paraMap, $urlencode){
 $buff = "";
 ksort($paraMap);
 foreach ($paraMap as $k => $v){
   if($urlencode)
   {
   $v = urlencode($v);
  }
  $buff .= $k . "=" . $v . "&";
 }
 $reqPar;
 if (strlen($buff) > 0){
  $reqPar = substr($buff, 0, strlen($buff)-1);
 }
 return $reqPar;
 }
}