Add types for `uppy.once` method (#2965)

Co-authored-by: Merlijn Vos <merlijn@soverin.net>

packages/@uppy/aws-s3/src/index.js

@@ -15,8 +15,8 @@
  * will expire before some files can be uploaded.
  *
  * The long-term solution to this problem is to change the upload pipeline so that files
- * can be sent to the next step individually. That requires a breakig change, so it is
- * planned for Uppy v2.
+ * can be sent to the next step individually. That requires a breaking change, so it is
+ * planned for some future Uppy version.
  *
  * In the mean time, this plugin is stuck with a hackier approach: the necessary parts
  * of the XHRUpload implementation were copied into this plugin, as the MiniXHRUpload

packages/@uppy/core/types/index.d.ts

@@ -147,17 +147,17 @@ declare module Uppy {
 
   type UploadHandler = (fileIDs: string[]) => Promise<void>
 
+  type UploadSuccessCallback<T> = (file: UppyFile<T>, body: any, uploadURL: string) => void
+  type UploadCompleteCallback<T> = (result: UploadResult<T>) => void
+
   class Uppy<TUseStrictTypes extends TypeChecking = TypeChecking> {
     constructor(opts?: UppyOptions)
-    on<TMeta extends IndexedObject<any> = {}>(
-      event: 'upload-success',
-      callback: (file: UppyFile<TMeta>, body: any, uploadURL: string) => void
-    ): this
-    on<TMeta extends IndexedObject<any> = {}>(
-      event: 'complete',
-      callback: (result: UploadResult<TMeta>) => void
-    ): this
+    on<TMeta extends IndexedObject<any> = {}>(event: 'upload-success', callback: UploadSuccessCallback<TMeta>): this
+    on<TMeta extends IndexedObject<any> = {}>(event: 'complete', callback: UploadCompleteCallback<TMeta>): this
     on(event: Event, callback: (...args: any[]) => void): this
+    once<TMeta extends IndexedObject<any> = {}>(event: 'upload-success', callback: UploadSuccessCallback<TMeta>): this
+    once<TMeta extends IndexedObject<any> = {}>(event: 'complete', callback: UploadCompleteCallback<TMeta>): this
+    once(event: Event, callback: (...args: any[]) => void): this
     off(event: Event, callback: (...args: any[]) => void): this
     /**
      * For use by plugins only.

packages/@uppy/core/types/index.test-d.ts

@@ -81,13 +81,17 @@ import DefaultStore = require('@uppy/store-default')
   // can emit events with custom event types
   uppy.emit('dashboard:modal-closed', () => {})
 
-  // can register listners for internal events
+  // can register listeners for internal events
   uppy.on('upload', () => {})
   uppy.on('complete', () => {})
   uppy.on('error', () => {})
+  uppy.once('upload', () => {})
+  uppy.once('complete', () => {})
+  uppy.once('error', () => {})
 
-  // can register listners on custom events
+  // can register listeners on custom events
   uppy.on('dashboard:modal-closed', () => {})
+  uppy.once('dashboard:modal-closed', () => {})
 }
 
 {