Add the option to use FormData to encode the form elements (#153)

* Add the option to use FormData to encode the form elements

If the form's enctype attribute is set to "multipart/form-data",
use FormData to encode the form's elements.

lib/proto/attach-form.js

@@ -15,8 +15,7 @@ var formAction = function(el, event) {
   // Initialize requestOptions
   options.requestOptions = {
     requestUrl: el.getAttribute("action") || window.location.href,
-    requestMethod: el.getAttribute("method") || "GET",
-    requestParams: []
+    requestMethod: el.getAttribute("method") || "GET"
   }
 
   // create a testable virtual link of the form action
@@ -31,6 +30,22 @@ var formAction = function(el, event) {
 
   event.preventDefault()
 
+  if (el.enctype === "multipart/form-data") {
+    options.requestOptions.formData = new FormData(el)
+  }
+  else {
+    options.requestOptions.requestParams = parseFormElements(el)
+  }
+
+  el.setAttribute(attrState, "submit")
+
+  options.triggerElement = el
+  this.loadUrl(virtLinkElement.href, options)
+}
+
+function parseFormElements(el) {
+  var requestParams = []
+
   for (var elementKey in el.elements) {
     if (Number.isNaN(Number(elementKey))) {
       continue;
@@ -62,7 +77,7 @@ var formAction = function(el, event) {
         }
 
         for (var j = 0; j < values.length; j++) {
-          options.requestOptions.requestParams.push({
+          requestParams.push({
             name: encodeURIComponent(element.name),
             value: encodeURIComponent(values[j])
           })
@@ -71,10 +86,7 @@ var formAction = function(el, event) {
     }
   }
 
-  el.setAttribute(attrState, "submit")
-
-  options.triggerElement = el
-  this.loadUrl(virtLinkElement.href, options)
+  return requestParams
 }
 
 function checkIfShouldAbort(virtLinkElement, options) {

lib/send-request.js

@@ -6,6 +6,7 @@ module.exports = function(location, options, callback) {
   var requestOptions = options.requestOptions || {}
   var requestMethod = (requestOptions.requestMethod || "GET").toUpperCase()
   var requestParams = requestOptions.requestParams || null
+  var formData = requestOptions.formData || null;
   var requestPayload = null
   var request = new XMLHttpRequest()
   var timeout = options.timeout || 0
@@ -51,6 +52,9 @@ module.exports = function(location, options, callback) {
         break
     }
   }
+  else if (formData) {
+    requestPayload = formData
+  }
 
   // Add a timestamp as part of the query string if cache busting is enabled
   if (options.cacheBust) {