Merge pull request element-hq#978 from vector-im/bwindels/errorboundary

ErrorBoundary utility

Author: bwindels

src/utils/ErrorBoundary.ts

@@ -0,0 +1,82 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export const ErrorValue = Symbol("ErrorBoundary:Error");
+
+export class ErrorBoundary {
+    private _error?: Error;
+
+    constructor(private readonly errorCallback: (Error) => void) {}
+
+    /**
+     * Executes callback() and then runs errorCallback() on error.
+     * This will never throw but instead return `errorValue` if an error occured.
+     */
+    try<T>(callback: () => T): T | typeof ErrorValue;
+    try<T>(callback: () => Promise<T>): Promise<T | typeof ErrorValue> | typeof ErrorValue {
+        try {
+            let result: T | Promise<T | typeof ErrorValue> = callback();
+            if (result instanceof Promise) {
+                result = result.catch(err => {
+                    this._error = err;
+                    this.errorCallback(err);
+                    return ErrorValue;
+                });
+            }
+            return result;
+        } catch (err) {
+            this._error = err;
+            this.errorCallback(err);
+            return ErrorValue;
+        }
+    }
+
+    get error(): Error | undefined {
+        return this._error;
+    }
+}
+
+export function tests() {
+    return {
+        "catches sync error": assert => {
+            let emitted = false;
+            const boundary = new ErrorBoundary(() => emitted = true);
+            const result = boundary.try(() => {
+                throw new Error("fail!");
+            });
+            assert(emitted);
+            assert.strictEqual(result, ErrorValue);
+        },
+        "return value of callback is forwarded": assert => {
+            let emitted = false;
+            const boundary = new ErrorBoundary(() => emitted = true);
+            const result = boundary.try(() => {
+                return "hello";
+            });
+            assert(!emitted);
+            assert.strictEqual(result, "hello");
+        },
+        "catches async error": async assert => {
+            let emitted = false;
+            const boundary = new ErrorBoundary(() => emitted = true);
+            const result = await boundary.try(async () => {
+                throw new Error("fail!");
+            });
+            assert(emitted);
+            assert.strictEqual(result, ErrorValue);
+        }
+    }
+}