normalize linefeeds for textareas

As the native FormData implementation converts linefeeds (LF) provided through user input to CRLF, the polyfill should do the same.

FormData.js

@@ -103,6 +103,15 @@ if (typeof FormData === 'undefined' || !FormData.prototype.keys) {
       : [name + '', value + '']
   }
 
+  // normalize linefeeds for textareas
+  // https://html.spec.whatwg.org/multipage/form-elements.html#textarea-line-break-normalisation-transformation
+  function normalizeLinefeeds(value) {
+    if (typeof value === "string") {
+      value = value.replace(/\r\n/g, "\n").replace(/\n/g, "\r\n")
+    }
+    return value
+  }
+
   function each (arr, cb) {
     for (let i = 0; i < arr.length; i++) {
       cb(arr[i])
@@ -141,7 +150,8 @@ if (typeof FormData === 'undefined' || !FormData.prototype.keys) {
         } else if (elm.type === 'checkbox' || elm.type === 'radio') {
           if (elm.checked) self.append(elm.name, elm.value)
         } else {
-          self.append(elm.name, elm.value)
+          const value = elm.type === 'textarea' ? normalizeLinefeeds(elm.value) : elm.value
+          self.append(elm.name, value)
         }
       })
     }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "formdata-polyfill",
-  "version": "3.0.13",
+  "version": "3.0.14",
   "description": "HTML5 `FormData` polyfill for Browsers.",
   "main": "formdata.min.js",
   "scripts": {

test/test.js

@@ -169,6 +169,56 @@ window.File = new Proxy(nativeFile, {
       })
     })
 
+    describe('linebreaks', () => {
+      // Native FormData normalizes linefeeds in textareas to CRLF
+      // In order to be consistent the polyfill should do the same
+      it('Should convert LF to CRLF for textareas', () => {
+        // This can not be tested with 'create_form' as the function ignores \n
+        const form = document.createElement('form')
+        const textarea = document.createElement('textarea')
+        textarea.name = 'key'
+        textarea.value = '\n'
+        form.appendChild(textarea)
+        const fd = new FormData(form)
+        const value = fd.get('key')
+        assert.equal('\r\n', value)
+      })
+
+      it('Should convert CR to CRLF for textareas', () => {
+        const form = document.createElement('form')
+        const textarea = document.createElement('textarea')
+        textarea.name = 'key'
+        textarea.value = '\r'
+        form.appendChild(textarea)
+        const fd = new FormData(form)
+        const value = fd.get('key')
+        assert.equal('\r\n', value)
+      })
+
+      it('Should normalize mixed linefeeds to CRLF for textareas', () => {
+        const form = document.createElement('form')
+        const textarea = document.createElement('textarea')
+        textarea.name = 'key'
+        textarea.value = 'a\n\ra\r\na\n\r\n\r\n\r\n\na\r\r'
+        form.appendChild(textarea)
+        const fd = new FormData(form)
+        const value = fd.get('key')
+        assert.equal('a\r\n\r\na\r\na\r\n\r\n\r\n\r\n\r\na\r\n\r\n', value)
+      })
+
+      it('Should not convert LF to CRLF when provided by append', () => {
+        const fd = create_formdata(['key', '\n'])
+        const value = fd.get('key')
+        assert.equal('\n', value)
+      })
+
+      it('Should not convert CR to CRLF when provided by append', () => {
+        const fd = create_formdata(['key', '\r'])
+        const value = fd.get('key')
+        assert.equal('\r', value)
+      })
+    })
+
     describe('disabled', () => {
       it('Shold not include disabled fields', () => {
         const fd = create_form(