diff --git a/README.md b/README.md
index f92d8a7..8e940d8 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,20 @@ npm install graphql-client -S
 
 ## How To
 ```javascript
-var client = require('graphql-client')({url: 'http://your-host/graphql'})
+var client = require('graphql-client')({
+  url: 'http://your-host/graphql',
+
+  // before request hook
+  onRequest (req) {
+    // Do whatever you want with `req`, e.g. add JWT auth header
+    req.headers.set('Authentication', 'Bearer ' + token)
+  },
+
+  // response hook
+  onResponse (res) {
+    ...
+  }
+})
 
 var query = `
   query search ($query: String, $from: Int, $limit: Int) {
diff --git a/index.js b/index.js
index 38b2cb7..a70d0f0 100644
--- a/index.js
+++ b/index.js
@@ -8,7 +8,7 @@ function highlightQuery (query, errors) {
 
   query.split('\n').forEach(function (row, index) {
     var line = index + 1
-    var lineErrors = locations.filter(function (loc) { return loc.line === line })
+    var lineErrors = locations.filter(function (loc) { return loc && loc.line === line })
 
     queryHighlight += row + '\n'
 
@@ -40,7 +40,7 @@ module.exports = function (params) {
       var headers = new Headers()
       headers.append('Content-Type', 'application/json')
 
-      return fetch(params.url, {
+      var req = {
         method: 'POST',
         body: JSON.stringify({
           query: query,
@@ -48,7 +48,12 @@ module.exports = function (params) {
         }),
         headers: headers,
         credentials: params.credentials
-      }).then(function (res) {
+      }
+
+      if (params.onRequest) params.onRequest(req)
+
+      return fetch(params.url, req).then(function (res) {
+        if (params.onResponse) params.onResponse(res)
         return res.json()
       }).then(function (data) {
         if (data.errors && data.errors.length) {