jsapi支付实现过程比较简单。
开发前必备:
1，已申请公众平台账号，并且开通微信支付认证功能。
2，获取appid
3, 已申请商户平台，需要拿到商户号。

    //公众号 appid private $appid = EVERY_APPID;//商户号private $mch_id = '151****';//支付回调private $notify_url = '配置自己服务器调用域名/notify_url';/*** 立即支付*/public function immediatel_pay(){   $openid = input('openid');//调用接口传递if(empty($openid)){return json(['code'=>1000,'msg'=>'openid不能为空']);}//生成订单号$order_no = $this->create_order_on();//支付金额 单位 元$pay_money = 0.01;$pay_result = $this->wx_jsapi($order_no,'定金支付成功',$openid,$pay_money);//入库try {//录入数据库信息} catch (\Exception $e) {return json(['code'=>1000,'msg'=>'下单失败,请重新下单']);}}/*** 生成订单号*/private function create_order_on(){$order_id_main = date('YmdHis') . rand(10000000,99999999);$order_id_len = strlen($order_id_main);$order_id_sum = 0;for($i=0; $i<$order_id_len; $i++){$order_id_sum += (int)(substr($order_id_main,$i,1));}$osn = $order_id_main . str_pad((100 - $order_id_sum % 100) % 100,2,'0',STR_PAD_LEFT);return $osn;}
private function wx_jsapi($order_no,$body,$openid,$total_fee){// echo '333';// exit;$request_url = "https://api.mch.weixin.qq.com/pay/unifiedorder";//接口链接//签名数据$sign_data = ['appid' => $this->appid, //公众号appid'mch_id' => $this->mch_id,  //商户号'nonce_str' => $this->createNoncestr(),'body' => $body, 'out_trade_no' => $order_no, //商户订单号'total_fee' => $total_fee*100, //标价金额 分'notify_url' => $this->notify_url,'trade_type' => 'JSAPI','openid' => $openid   //授权获取的openid];$sign_data['sign'] = makeSign($sign_data);$request_param = ArrToXml($sign_data);$result_xml = $this->https_request($request_url,$request_param);$result_arr = XmlToArr($result_xml);//获取预支付交易会话标识if($result_arr['return_code'] == 'SUCCESS' && $result_arr['result_code'] == 'SUCCESS'){$timeStamp = time();//返回前端 $arr$arr = array("appId" => $this->appid,"timeStamp" => "$timeStamp",        //这里是字符串的时间戳，不是int，所以需加引号"nonceStr" => $this->createNoncestr(),"package" => "prepay_id=" . $result_arr['prepay_id'],"signType" => 'MD5',);$arr['paySign'] = makeSign($arr);}else{}return $arr;}/***  作用：产生随机字符串，不长于32位*/private function createNoncestr( $length = 32 ){$chars = "abcdefghijklmnopqrstuvwxyz0123456789";$str ="";for ( $i = 0; $i < $length; $i++ )  {$str.= substr($chars, mt_rand(0, strlen($chars)-1), 1);}return $str;}/*** 模拟 http 请求* @param  String $url  请求网址* @param  Array  $data 数据*/private function https_request($url, $data = null){// curl 初始化$curl = curl_init();// curl 设置curl_setopt($curl, CURLOPT_URL, $url);curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, FALSE);// 判断 $data get  or postif ( !empty($data) ) {curl_setopt($curl, CURLOPT_POST, 1);curl_setopt($curl, CURLOPT_POSTFIELDS, $data);}curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);// 执行$res = curl_exec($curl);curl_close($curl);return $res;}

数组转xml

 if(!is_array($arr) || count($arr) == 0) return '';$xml = "<xml>";foreach ($arr as $key=>$val){if (is_numeric($val)){$xml.="<".$key.">".$val."</".$key.">";}else{$xml.="<".$key."><![CDATA[".$val."]]></".$key.">";}}$xml.="</xml>";

xml转数组

 libxml_disable_entity_loader(true);$arr = json_decode(json_encode(simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOCDATA)), true);

生成签名

/*** 生成签名* @return 签名，*/function makeSign($data){unset($data['sign']);foreach ($data as $k => $v) {$Parameters[$k] = $v;}//签名步骤一：按字典序排序参数ksort($Parameters);$String = formatBizQueryParaMap($Parameters, false);//签名步骤二：在string后加入KEY$String = $String . "&key=" . WX_KEY;//签名步骤三：MD5加密$String = md5($String);//签名步骤四：所有字符转为大写$result_ = strtoupper($String);return $result_;}

异步调用

//异步通知public function notify_url(){//接收数据$input_xml = file_get_contents("php://input");try {$input_arr = XmlToArr($input_xml);if(!isset($input_arr['sign'])){\think\Log::write('WxJsapi---'.var_export('签名未找到',true). 'debug');exit;}//验证签名$sign_2 = makeSign($input_arr);if($input_arr['sign'] != $sign_2){\think\Log::write('WxJsapi---'.var_export('签名错误',true). 'debug');exit;} //修改订单状态$where = ['order_no'=>$input_arr['out_trade_no'],'status'=>1];db('bargain_money_order')->where($where)->find()；} catch ( \Exception $e) {\think\Log::write('WxJsapi---异步通知-------notify_url-- 捕获异常---'.var_export($e->getMessage(),true). 'debug');}}

进行了分拆，可以组合使用。