Create setErrorMessage (#280)

Author: castrodd

src/errors.ts

@@ -9,6 +9,13 @@ export interface AzFuncError {
     isAzureFunctionsSystemError: boolean;
 }
 
+export interface ValidatedError extends Error, Partial<AzFuncError> {
+    /**
+     * Use `trySetErrorMessage` to set the error message
+     */
+    readonly message: string;
+}
+
 export class AzFuncSystemError extends Error {
     isAzureFunctionsSystemError = true;
 }
@@ -27,22 +34,8 @@ export class ReadOnlyError extends AzFuncTypeError {
     }
 }
 
-export function ensureErrorType(err: unknown): Error & Partial<AzFuncError> {
+export function ensureErrorType(err: unknown): ValidatedError {
     if (err instanceof Error) {
-        const writable = Object.getOwnPropertyDescriptor(err, 'message')?.writable;
-        if (!writable) {
-            // The motivation for this branch can be found in the below issue:
-            // https://github.com/Azure/azure-functions-nodejs-library/issues/205
-            let readableMessage = err.message;
-            Object.defineProperty(err, 'message', {
-                get() {
-                    return readableMessage;
-                },
-                set(val: string) {
-                    readableMessage = val;
-                },
-            });
-        }
         return err;
     } else {
         let message: string;
@@ -59,6 +52,14 @@ export function ensureErrorType(err: unknown): Error & Partial<AzFuncError> {
     }
 }
 
+export function trySetErrorMessage(err: Error, message: string): void {
+    try {
+        err.message = message;
+    } catch {
+        // If we can't set the message, we'll keep the error as is
+    }
+}
+
 /**
  * This is mostly for callbacks where `null` or `undefined` indicates there is no error
  * By contrast, anything thrown/caught is assumed to be an error regardless of what it is

test/errors.test.ts

@@ -3,7 +3,7 @@
 
 import 'mocha';
 import { expect } from 'chai';
-import { ensureErrorType } from '../src/errors';
+import { ensureErrorType, trySetErrorMessage } from '../src/errors';
 
 describe('ensureErrorType', () => {
     it('null', () => {
@@ -42,6 +42,13 @@ describe('ensureErrorType', () => {
         expect(ensureErrorType(actualError)).to.equal(actualError);
     });
 
+    it('modify error message', () => {
+        const actualError = new Error('test2');
+        trySetErrorMessage(actualError, 'modified message');
+
+        expect(actualError.message).to.equal('modified message');
+    });
+
     it('readonly error', () => {
         class ReadOnlyError extends Error {
             get message(): string {
@@ -55,10 +62,11 @@ describe('ensureErrorType', () => {
         expect(() => (actualError.message = 'exception')).to.throw();
 
         const wrappedError = ensureErrorType(actualError);
-        wrappedError.message = 'Readonly error has been modified';
+        const message = 'Readonly error has not been modified';
+        trySetErrorMessage(wrappedError, message);
 
-        expect(wrappedError.message).to.equal('Readonly error has been modified');
-        expect(wrappedError.stack).to.contain('Readonly error has been modified');
+        expect(wrappedError.message).to.equal('a readonly message');
+        expect(wrappedError.stack).to.not.contain('Readonly error has been modified');
     });
 
     function validateError(actual: Error, expectedMessage: string): void {