diff --git a/index.js b/index.js
index 0776514..966a5e5 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,7 @@
 
   function defaults (target, obj) {
     for (var prop in obj) target[prop] = target[prop] || obj[prop]
+    return target
   }
 
   function getQuery (queryParams) {
@@ -11,10 +12,30 @@
     return '?' + arr.join('&')
   }
 
+  function identity(arg) { return arg }
+
+  var responseHandlers = {
+    'json': function(response) { return response.json() },
+    'text': function(response) { return response.text() },
+    'response': true
+  }
+
+  var encodeHandlers = {
+    'json': JSON.stringify,
+    'noop': identity,
+    true: identity,
+    false: identity,
+  }
+
   function _fetch (method, url, opts, data, queryParams) {
+    // Use a shallow copy of opts parameter and opts.header subfield
+    opts = defaults({}, opts)
     opts.method = method
-    opts.headers = opts.headers || {}
-    opts.responseAs = (opts.responseAs && ['json', 'text', 'response'].indexOf(opts.responseAs) >= 0) ? opts.responseAs : 'json'
+    opts.headers = defaults({}, opts.headers || {})
+
+    if (opts.responseAs !== true && typeof opts.responseAs !== 'function') {
+      opts.responseAs = responseHandlers[opts.responseAs] || responseHandlers.json
+    }
 
     defaults(opts.headers, {
       'Accept': 'application/json',
@@ -26,23 +47,28 @@
     }
 
     if (data) {
-        opts.body = JSON.stringify(data);
-    } else {
-        delete opts.body;
+      if (typeof opts.encodeAs !== 'function') {
+        opts.encodeAs = encodeHandlers[opts.encodeAs] || encodeHandlers.json
+      }
+      opts.body = opts.encodeAs(data)
     }
 
     return fetchival.fetch(url, opts)
       .then(function (response) {
         if (response.status >= 200 && response.status < 300) {
-          if(opts.responseAs=="response")
+          if(opts.responseAs===true)
             return response
           if (response.status == 204)
             return null;
-          return response[opts.responseAs]();
+          return opts.responseAs(response);
+        }
+        if(typeof opts.errorAs !== 'function') {
+          var err = new Error(response.statusText)
+          err.response = response
+          throw err
+        } else {
+          throw opts.errorAs(response)
         }
-        var err = new Error(response.statusText)
-        err.response = response
-        throw err
       })
   }
 
@@ -61,20 +87,20 @@
       return _fetch('GET', url, opts, null, queryParams)
     }
 
-    _.post = function (data) {
-      return _fetch('POST', url, opts, data)
+    _.post = function (data, queryParams) {
+      return _fetch('POST', url, opts, data, queryParams)
     }
 
-    _.put = function (data) {
-      return _fetch('PUT', url, opts, data)
+    _.put = function (data, queryParams) {
+      return _fetch('PUT', url, opts, data, queryParams)
     }
 
-    _.patch = function (data) {
-      return _fetch('PATCH', url, opts, data)
+    _.patch = function (data, queryParams) {
+      return _fetch('PATCH', url, opts, data, queryParams)
     }
 
-    _.delete = function () {
-      return _fetch('DELETE', url, opts)
+    _.delete = function (queryParams) {
+      return _fetch('DELETE', url, opts, null, queryParams)
     }
 
     return _
@@ -83,6 +109,8 @@
   // Expose fetch so that other polyfills can be used
   // Bind fetch to window to avoid TypeError: Illegal invocation
   fetchival.fetch = typeof fetch !== 'undefined' ? fetch.bind(window) : null
+  fetchival.responseHandlers = responseHandlers
+  fetchival.encodeHandlers = encodeHandlers
 
   // Support CommonJS, AMD & browser
   if (typeof exports === 'object')
diff --git a/test/tests.js b/test/tests.js
index dbbb6e7..482a8ac 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -17,6 +17,30 @@ var requestText = fetchival('http://jsonplaceholder.typicode.com', {
   responseAs: 'text'
 })
 
+fetchival.responseHandlers['registered-example'] = function(response) {
+  return response.json()
+    .then(function (json) {
+      return {kind: 'registered-example', json: json, response: response}
+    })
+}
+
+var requestRegisteredExample = fetchival('http://jsonplaceholder.typicode.com', {
+  mode: 'cors',
+  headers: { 'X-TEST': 'test' },
+  responseAs: 'registered-example'
+})
+
+var requestCustomExample = fetchival('http://jsonplaceholder.typicode.com', {
+  mode: 'cors',
+  headers: { 'X-TEST': 'test' },
+  responseAs: function(response) {
+    return response.json()
+      .then(function (json) {
+        return {kind: 'custom', json: json, response: response}
+      })
+  }
+})
+
 describe('fetchival', function () {
   this.timeout(5000)
   this.slow(5000)
@@ -135,4 +159,37 @@ describe('fetchival', function () {
         })
     })
   })
+
+  describe('requestCustomExample(posts/1/comments)', function () {
+    var posts = requestCustomExample('posts')
+    var comments = posts(1 + '/comments')
+
+    it('should #get()', function (done) {
+      comments
+        .get()
+        .then(function (extendedReponseObj) {
+          assert.equal('custom', extendedReponseObj.kind)
+          assert(extendedReponseObj.response.ok)
+          assert(extendedReponseObj.json.length)
+          done()
+        })
+    })
+  })
+
+  describe('requestRegisteredExample(posts/1/comments)', function () {
+    var posts = requestRegisteredExample('posts')
+    var comments = posts(1 + '/comments')
+
+    it('should #get()', function (done) {
+      comments
+        .get()
+        .then(function (extendedReponseObj) {
+          assert.equal('registered-example', extendedReponseObj.kind)
+          assert(extendedReponseObj.response.ok)
+          assert(extendedReponseObj.json.length)
+          done()
+        })
+    })
+  })
+
 })