implemented onConfig

Author: cyfung1031

index.d.ts

@@ -97,6 +97,7 @@ interface XhrErrorHandler extends XhrHandler {
 }
 
 interface Proxy {
+  onConfig?: (config: XhrRequestConfig, xhrProxy: Hooks) => boolean | void,
   onRequest?: (config: XhrRequestConfig, handler: XhrRequestHandler) => void,
   onResponse?: (response: XhrResponse, handler: XhrResponseHandler) => void,
   onError?: (err: XhrError, handler: XhrErrorHandler) => void,

src/xhr-proxy.js

@@ -102,7 +102,9 @@ var ErrorHandler = makeHandler(function (error) {
 });
 
 function proxyAjax(proxy, win) {
-  var onRequest = proxy.onRequest,
+  var onConfig = proxy.onConfig,
+    onRequest = null,
+    onRequest_ = proxy.onRequest,
     onResponse = proxy.onResponse,
     onError = proxy.onError;
 
@@ -187,6 +189,10 @@ function proxyAjax(proxy, win) {
       // 所以我们在send拦截函数中再手动调用open，因此返回true阻止xhr.open调用。
       //
       // 如果没有请求拦截器，则不用阻断xhr.open调用
+      onRequest = onRequest_;
+      if (onConfig) {
+        if (onConfig(config, this) === false) onRequest = null;
+      }
       if (onRequest) return true;
     },
     send: function (args, xhr) {