feat: propagate data.cause as cause in JsonRpcError constructor

jest.config.js

@@ -45,10 +45,10 @@ module.exports = {
   // An object that configures minimum threshold enforcement for coverage results
   coverageThreshold: {
     global: {
-      branches: 92.64,
-      functions: 94.44,
-      lines: 92.85,
-      statements: 92.85,
+      branches: 91.89,
+      functions: 94.59,
+      lines: 92.42,
+      statements: 92.42,
     },
   },
 

src/__fixtures__/errors.ts

@@ -1,7 +1,11 @@
 import { rpcErrors } from '..';
 
-export const dummyData = { foo: 'bar' };
 export const dummyMessage = 'baz';
+export const dummyData = { foo: 'bar' };
+export const dummyDataWithCause = {
+  foo: 'bar',
+  cause: { message: dummyMessage },
+};
 
 export const invalidError0 = 0;
 export const invalidError1 = ['foo', 'bar', 3];

src/classes.ts

@@ -6,7 +6,7 @@ import { isPlainObject } from '@metamask/utils';
 import safeStringify from 'fast-safe-stringify';
 
 import type { OptionalDataWithOptionalCause } from './utils';
-import { serializeCause } from './utils';
+import { dataHasCause, serializeCause } from './utils';
 
 export type { SerializedJsonRpcError };
 
@@ -19,6 +19,9 @@ export type { SerializedJsonRpcError };
 export class JsonRpcError<
   Data extends OptionalDataWithOptionalCause,
 > extends Error {
+  // The `cause` field can be removed when tsconfig lib and/or target have changed to >=es2022
+  public cause?: unknown;
+
   public code: number;
 
   public data?: Data;
@@ -32,11 +35,23 @@ export class JsonRpcError<
       throw new Error('"message" must be a non-empty string.');
     }
 
-    super(message);
-    this.code = code;
+    if (dataHasCause(data)) {
+      // @ts-expect-error - Error class does accept options argument depending on runtime, but types are mapping to oldest supported
+      super(message, { cause: data.cause });
+
+      // Browser backwards-compatibility fallback
+      if (!Object.prototype.hasOwnProperty.call(this, 'cause')) {
+        Object.assign(this, { cause: data.cause });
+      }
+    } else {
+      super(message);
+    }
+
     if (data !== undefined) {
       this.data = data;
     }
+
+    this.code = code;
   }
 
   /**

src/errors.test.ts

@@ -3,6 +3,8 @@ import { assert, isPlainObject } from '@metamask/utils';
 import { rpcErrors, providerErrors, errorCodes } from '.';
 import {
   dummyData,
+  dummyDataWithCause,
+  dummyMessage,
   CUSTOM_ERROR_MESSAGE,
   SERVER_ERROR_CODE,
   CUSTOM_ERROR_CODE,
@@ -97,6 +99,21 @@ describe('rpcErrors', () => {
     },
   );
 
+  it.each(Object.entries(rpcErrors).filter(([key]) => key !== 'server'))(
+    '%s propagates data.cause if set',
+    (key, value) => {
+      const createError = value as any;
+      const error = createError({
+        message: null,
+        data: Object.assign({}, dummyDataWithCause),
+      });
+      // @ts-expect-error TypeScript does not like indexing into this with the key
+      const rpcCode = errorCodes.rpc[key];
+      expect(error.message).toBe(getMessageFromCode(rpcCode));
+      expect(error.cause.message).toBe(dummyMessage);
+    },
+  );
+
   it('serializes a cause', () => {
     const error = rpcErrors.invalidInput({
       data: {
@@ -156,6 +173,21 @@ describe('providerErrors', () => {
     },
   );
 
+  it.each(Object.entries(providerErrors).filter(([key]) => key !== 'custom'))(
+    '%s propagates data.cause if set',
+    (key, value) => {
+      const createError = value as any;
+      const error = createError({
+        message: null,
+        data: Object.assign({}, dummyDataWithCause),
+      });
+      // @ts-expect-error TypeScript does not like indexing into this with the key
+      const providerCode = errorCodes.provider[key];
+      expect(error.message).toBe(getMessageFromCode(providerCode));
+      expect(error.cause.message).toBe(dummyMessage);
+    },
+  );
+
   it('custom returns appropriate value', () => {
     const error = providerErrors.custom({
       code: CUSTOM_ERROR_CODE,

src/index.ts

@@ -1,5 +1,10 @@
 export { JsonRpcError, EthereumProviderError } from './classes';
-export { serializeCause, serializeError, getMessageFromCode } from './utils';
+export {
+  dataHasCause,
+  serializeCause,
+  serializeError,
+  getMessageFromCode,
+} from './utils';
 export type {
   DataWithOptionalCause,
   OptionalDataWithOptionalCause,

src/utils.test.ts

@@ -16,7 +16,7 @@ import {
   dummyMessage,
   dummyData,
 } from './__fixtures__';
-import { getMessageFromCode, serializeError } from './utils';
+import { dataHasCause, getMessageFromCode, serializeError } from './utils';
 
 const rpcCodes = errorCodes.rpc;
 
@@ -310,3 +310,23 @@ describe('serializeError', () => {
     });
   });
 });
+
+describe('dataHasCause', () => {
+  it('returns false for invalid data types', () => {
+    [undefined, null, 'hello', 1234].forEach((data) => {
+      const result = dataHasCause(data);
+      expect(result).toBe(false);
+    });
+  });
+  it('returns false for invalid cause types', () => {
+    [undefined, null, 'hello', 1234].forEach((cause) => {
+      const result = dataHasCause({ cause });
+      expect(result).toBe(false);
+    });
+  });
+  it('returns true when cause is object', () => {
+    const data = { cause: {} };
+    const result = dataHasCause(data);
+    expect(result).toBe(true);
+  });
+});

src/utils.ts

@@ -211,3 +211,16 @@ function serializeObject(object: RuntimeObject): Json {
     {},
   );
 }
+
+/**
+ * Returns true if supplied error data has a usable `cause` property; false otherwise.
+ *
+ * @param data - Optional data to validate.
+ * @returns Whether cause property is present and an object.
+ */
+export function dataHasCause(data: unknown): data is {
+  [key: string]: Json | unknown;
+  cause: object;
+} {
+  return isObject(data) && hasProperty(data, 'cause') && isObject(data.cause);
+}

tsconfig.json

@@ -3,6 +3,7 @@
     "esModuleInterop": true,
     "exactOptionalPropertyTypes": true,
     "forceConsistentCasingInFileNames": true,
+    // Reminder: Remove custom `cause` field from JsonRpcError when enabling es2022
     "lib": ["ES2020"],
     "module": "CommonJS",
     "moduleResolution": "node",