core: Add `allowMultipleUploads: false` option.

packages/@uppy/core/src/index.js

@@ -54,6 +54,7 @@ class Uppy {
     const defaultOptions = {
       id: 'uppy',
       autoProceed: false,
+      allowMultipleUploads: true,
       debug: false,
       restrictions: {
         maxFileSize: null,
@@ -118,11 +119,12 @@ class Uppy {
       plugins: {},
       files: {},
       currentUploads: {},
+      allowNewUpload: true,
       capabilities: {
         resumableUploads: false
       },
       totalProgress: 0,
-      meta: Object.assign({}, this.opts.meta),
+      meta: { ...this.opts.meta },
       info: {
         isHidden: true,
         type: 'info',
@@ -1025,6 +1027,11 @@ class Uppy {
    * @return {string} ID of this upload.
    */
   _createUpload (fileIDs) {
+    const { allowNewUpload, currentUploads } = this.getState()
+    if (!allowNewUpload) {
+      throw new Error('Cannot create a new upload: already uploading.')
+    }
+
     const uploadID = cuid()
 
     this.emit('upload', {
@@ -1033,20 +1040,25 @@ class Uppy {
     })
 
     this.setState({
-      currentUploads: Object.assign({}, this.getState().currentUploads, {
+      allowNewUpload: this.opts.allowMultipleUploads !== false,
+
+      currentUploads: {
+        ...currentUploads,
         [uploadID]: {
           fileIDs: fileIDs,
           step: 0,
           result: {}
         }
-      })
+      }
     })
 
     return uploadID
   }
 
   _getUpload (uploadID) {
-    return this.getState().currentUploads[uploadID]
+    const { currentUploads } = this.getState()
+
+    return currentUploads[uploadID]
   }
 
   /**

packages/@uppy/core/src/index.test.js

@@ -152,6 +152,7 @@ describe('src/Core', () => {
         capabilities: { resumableUploads: false },
         files: {},
         currentUploads: {},
+        allowNewUpload: true,
         foo: 'baar',
         info: { isHidden: true, message: '', type: 'info' },
         meta: {},
@@ -175,6 +176,7 @@ describe('src/Core', () => {
         capabilities: { resumableUploads: false },
         files: {},
         currentUploads: {},
+        allowNewUpload: true,
         foo: 'bar',
         info: { isHidden: true, message: '', type: 'info' },
         meta: {},
@@ -187,6 +189,7 @@ describe('src/Core', () => {
         capabilities: { resumableUploads: false },
         files: {},
         currentUploads: {},
+        allowNewUpload: true,
         foo: 'baar',
         info: { isHidden: true, message: '', type: 'info' },
         meta: {},
@@ -204,6 +207,7 @@ describe('src/Core', () => {
         capabilities: { resumableUploads: false },
         files: {},
         currentUploads: {},
+        allowNewUpload: true,
         foo: 'bar',
         info: { isHidden: true, message: '', type: 'info' },
         meta: {},
@@ -231,6 +235,7 @@ describe('src/Core', () => {
       capabilities: { resumableUploads: false },
       files: {},
       currentUploads: {},
+      allowNewUpload: true,
       error: null,
       foo: 'bar',
       info: { isHidden: true, message: '', type: 'info' },
@@ -289,6 +294,7 @@ describe('src/Core', () => {
       capabilities: { resumableUploads: false },
       files: {},
       currentUploads: {},
+      allowNewUpload: true,
       error: null,
       info: { isHidden: true, message: '', type: 'info' },
       meta: {},
@@ -736,6 +742,34 @@ describe('src/Core', () => {
         expect(err).toMatchObject(new Error('Not starting the upload because onBeforeUpload returned false'))
       })
     })
+
+    it('only allows a single upload() batch when allowMultipleUploads: false', async () => {
+      const core = new Core({ allowMultipleUploads: false })
+      core.addFile({
+        source: 'jest',
+        name: 'foo.jpg',
+        type: 'image/jpeg',
+        data: new File([sampleImage], { type: 'image/jpeg' })
+      })
+      core.addFile({
+        source: 'jest',
+        name: 'bar.jpg',
+        type: 'image/jpeg',
+        data: new File([sampleImage], { type: 'image/jpeg' })
+      })
+
+      await expect(core.upload()).resolves.toBeDefined()
+
+      core.addFile({
+        source: 'jest',
+        name: '123.foo',
+        type: 'image/jpeg',
+        data: new File([sampleImage], { type: 'image/jpeg' })
+      })
+      await expect(core.upload()).rejects.toThrow(
+        /Cannot create a new upload: already uploading\./
+      )
+    })
   })
 
   describe('removing a file', () => {