Add getStringFromErrorLike utility

Summary: I've found myself having to extract strings from things that *might* be Errors more than once. Centralising this so it's consistent and correct everywhere.

Reviewed By: danielbuechele

Differential Revision: D15536034

fbshipit-source-id: 8e054dd6122aff10f0aacdfaed65125df0aea99f

src/plugins/databases/index.js

@@ -16,6 +16,7 @@ import {
   Button,
   ButtonGroup,
   Input,
+  getStringFromErrorLike,
 } from 'flipper';
 import {Component} from 'react';
 import type {
@@ -757,7 +758,7 @@ export default class DatabasesPlugin extends FlipperPlugin<
             ) : null}
           </FlexRow>
         </Toolbar>
-        {this.state.error && JSON.stringify(this.state.error)}
+        {this.state.error && getStringFromErrorLike(this.state.error)}
       </FlexColumn>
     );
   }

src/utils/errors.js

@@ -0,0 +1,16 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+export function getStringFromErrorLike(e: any) {
+  if (typeof e == 'string') {
+    return e;
+  } else if (e instanceof Error) {
+    return e.message;
+  } else {
+    return JSON.stringify(e);
+  }
+}

src/utils/index.js

@@ -6,3 +6,4 @@
  */
 
 export {default as textContent} from './textContent.js';
+export {getStringFromErrorLike} from './errors.js';