fix: Source.on is not a function for t:variables

dist/Types/Messages/Messages.d.ts

@@ -18,7 +18,14 @@ export type CustomFile = {
     [key: string]: unknown;
 };
 export type MessageAttachment = CustomFile | CustomFile[] | File | File[] | string | CustomFileData | CustomFileData[];
-export type FormDataInputValue = MimeMessage | CustomFileData | string | string[] | boolean | MessageAttachment | undefined | number;
+export type FormDataInputValue = MimeMessage | CustomFileData | string | string[] | boolean | MessageAttachment | undefined | number | JsonObject;
+export type JsonPrimitive = string | number | boolean | null;
+export type JsonArray = Json[];
+export type JsonObject = {
+    [key: string]: Json;
+};
+export type JsonComposite = JsonArray | JsonObject;
+export type Json = JsonPrimitive | JsonComposite;
 export type MailgunMessageContent = AtLeastOneKeyPresent<{
     /**
      * Body of the message. (text version)
@@ -85,6 +92,11 @@ export type MailgunMessageData = MailgunMessageContent & {
      * in the text part of the message in case of template sending
      */
     't:text'?: boolean | 'yes' | 'no';
+    /**
+     * A valid JSON-encoded dictionary used as the input for template variable expansion.
+     * See [Templates](https://documentation.mailgun.com/en/latest/api-templates.html#api-templates) for more information.
+     */
+    't:variables'?: string | JsonObject;
     /**
      * Tag string. See [Tagging](https://documentation.mailgun.com/en/latest/user_manual.html#tagging) for more information.
      */

lib/Classes/common/FormDataBuilder.ts

@@ -185,6 +185,14 @@ class FormDataBuilder {
   ): void {
     const addValueBasedOnFD = (fdKey: string, fdValue: FormDataInputValue): void => {
       if (this.isFormDataPackage(formDataAcc)) {
+        if (typeof fdValue === 'object') {
+          // eslint-disable-next-line no-console
+          console.warn('The received value is an object. \n'
+          + '"JSON.Stringify" will be used to avoid TypeError \n'
+          + 'To remove this warning: \n'
+          + 'Consider switching to built-in FormData or converting the value on your own.\n');
+          return formDataAcc.append(fdKey, JSON.stringify(fdValue));
+        }
         return formDataAcc.append(fdKey, fdValue);
       }
       if (typeof fdValue === 'string') {

lib/Types/Messages/Messages.ts

@@ -1,3 +1,4 @@
+/* eslint-disable no-use-before-define */
 /**
  * Ensures the object has least one key present and not undefined
  *
@@ -41,6 +42,13 @@
   | MessageAttachment
   | undefined
   | number // doc says it should be auto-converted https://developer.mozilla.org/en-US/docs/Web/API/FormData/append
+  | JsonObject
+
+export type JsonPrimitive = string | number | boolean | null;
+export type JsonArray = Json[];
+export type JsonObject = { [key: string]: Json };
+export type JsonComposite = JsonArray | JsonObject;
+export type Json = JsonPrimitive | JsonComposite;
 
 export type MailgunMessageContent = AtLeastOneKeyPresent<{
     /**
@@ -107,7 +115,7 @@
      *
      * You can post multiple `inline` values.
      */
     inline?: any;
 
     /**
      * Use this parameter to send a message to specific version of a template
@@ -120,6 +128,12 @@
      */
     't:text'?: boolean | 'yes' | 'no';
 
+    /**
+     * A valid JSON-encoded dictionary used as the input for template variable expansion.
+     * See [Templates](https://documentation.mailgun.com/en/latest/api-templates.html#api-templates) for more information.
+     */
+    't:variables'?: string | JsonObject;
+
     /**
      * Tag string. See [Tagging](https://documentation.mailgun.com/en/latest/user_manual.html#tagging) for more information.
      */

test/formDataBuilder.test.ts

@@ -104,6 +104,18 @@ describe('FormDataBuilder', function () {
       expect(data).include('Content-Disposition: form-data; name="attachment"; filename="file"');
       expect(data).include('Content-Type: application/octet-stream');
     });
+
+    it('Converts object to String value', async () => {
+      // Prevents TypeError: source.on is not a function for form-data package
+      const formDataWithValue = builder.createFormData({
+        't:variables': {
+          testProp: 'testValue'
+        }
+      }) as NodeFormData;
+      const data = formDataWithValue.getBuffer().toString();
+      expect(data).include('Content-Disposition: form-data; name="t:variables"');
+      expect(data).include('{"testProp":"testValue"}');
+    });
   });
 
   if (global.FormData) {