Active Storage: Fix direct uploads in IE 11

Fixes #31531
Closes #31540

activestorage/app/javascript/activestorage/blob_record.js

@@ -22,14 +22,28 @@ export class BlobRecord {
     this.xhr.addEventListener("error", event => this.requestDidError(event))
   }
 
+  get status() {
+    return this.xhr.status
+  }
+
+  get response() {
+    const { responseType, response } = this.xhr
+    if (responseType == "json") {
+      return response
+    } else {
+      // Shim for IE 11: https://connect.microsoft.com/IE/feedback/details/794808
+      return JSON.parse(response)
+    }
+  }
+
   create(callback) {
     this.callback = callback
     this.xhr.send(JSON.stringify({ blob: this.attributes }))
   }
 
   requestDidLoad(event) {
-    const { status, response } = this.xhr
-    if (status >= 200 && status < 300) {
+    if (this.status >= 200 && this.status < 300) {
+      const { response } = this
       const { direct_upload } = response
       delete response.direct_upload
       this.attributes = response
@@ -41,7 +55,7 @@ export class BlobRecord {
   }
 
   requestDidError(event) {
-    this.callback(`Error creating Blob for "${this.file.name}". Status: ${this.xhr.status}`)
+    this.callback(`Error creating Blob for "${this.file.name}". Status: ${this.status}`)
   }
 
   toJSON() {