Refactoring

src/error/create.js

@@ -5,8 +5,7 @@ export const createErrorType = function (name, onCreate = defaultOnCreate) {
   const ErrorType = class extends Error {
     constructor(message, opts = {}) {
       validateOpts(opts)
-      const errorOpts = opts.cause === undefined ? {} : { cause: opts.cause }
-      super(message, errorOpts)
+      super(message, getErrorOpts(opts))
       // eslint-disable-next-line fp/no-this
       onCreate(this, getOnCreateOpts(this, opts))
     }
@@ -16,34 +15,8 @@ export const createErrorType = function (name, onCreate = defaultOnCreate) {
   return ErrorType
 }
 
-// Validate `error.name` looks like `ExampleError`.
-const validateErrorName = function (name) {
-  if (typeof name !== 'string') {
-    throw new TypeError(`Error name must be a string: ${name}`)
-  }
-
-  if (!name.endsWith(ERROR_NAME_END) || name === ERROR_NAME_END) {
-    throw new Error(`Error name "${name}" must end with "${ERROR_NAME_END}"`)
-  }
-
-  validateErrorNamePattern(name)
-}
-
-const validateErrorNamePattern = function (errorName) {
-  if (errorName[0] !== errorName.toUpperCase()[0]) {
-    throw new Error(
-      `Error name "${errorName}" must start with an uppercase letter.`,
-    )
-  }
-
-  if (!ERROR_NAME_REGEXP.test(errorName)) {
-    throw new Error(`Error name "${errorName}" must only contain letters.`)
-  }
-}
-
-const ERROR_NAME_END = 'Error'
-const ERROR_NAME_REGEXP = /[A-Z][a-zA-Z]*Error$/u
-
+// Due to `error.cause`, the second argument should always be a plain object
+// We enforce no third argument since this is cleaner.
 const validateOpts = function (opts) {
   if (typeof opts !== 'object' || opts === null) {
     throw new TypeError(
@@ -52,6 +25,11 @@ const validateOpts = function (opts) {
   }
 }
 
+// Passing `{ cause: undefined }` creates `error.cause`, unlike passing `{}`
+const getErrorOpts = function ({ cause }) {
+  return cause === undefined ? {} : { cause }
+}
+
 // When passing options to `onCreate()`, ignore keys that:
 //  - Would override `Object` prototype (`hasOwnProperty`, etc.) or `Error`
 //    prototype (`toString`)
@@ -76,18 +54,15 @@ const getOnCreateOpts = function (error, opts) {
 
 const { propertyIsEnumerable: isEnum } = Object.prototype
 
+// Uses `key in error` to handle any current and future error|object properties
 const shouldIgnoreKey = function (error, key) {
   return key in error || IGNORED_KEYS.has(key)
 }
 
 const IGNORED_KEYS = new Set(['errors', 'prototype'])
 
 // `onCreate(error, opts)` allows custom logic at initialization time.
-// The construction arguments are passed.
-//  - They can be validated, normalized, etc.
-//  - No third argument is passed. This enforces calling named parameters
-//    `new ErrorType('message', opts)` instead of positional ones, which is
-//    cleaner.
+// The construction `opts` are passed, i.e. can be validated, normalized, etc.
 // `onCreate()` is useful to assign error instance-specific properties.
 //  - Therefore, the default value just assign `opts`.
 // Properties that are error type-specific (i.e. same for all instances of that
@@ -110,6 +85,35 @@ const defaultOnCreate = function (error, opts) {
   Object.assign(error, opts)
 }
 
+// Validate `error.name` looks like `ExampleError` for consistency with
+// native error types and common practices that users might expect
+const validateErrorName = function (name) {
+  if (typeof name !== 'string') {
+    throw new TypeError(`Error name must be a string: ${name}`)
+  }
+
+  if (!name.endsWith(ERROR_NAME_END) || name === ERROR_NAME_END) {
+    throw new Error(`Error name "${name}" must end with "${ERROR_NAME_END}"`)
+  }
+
+  validateErrorNamePattern(name)
+}
+
+const validateErrorNamePattern = function (errorName) {
+  if (errorName[0] !== errorName.toUpperCase()[0]) {
+    throw new Error(
+      `Error name "${errorName}" must start with an uppercase letter.`,
+    )
+  }
+
+  if (!ERROR_NAME_REGEXP.test(errorName)) {
+    throw new Error(`Error name "${errorName}" must only contain letters.`)
+  }
+}
+
+const ERROR_NAME_END = 'Error'
+const ERROR_NAME_REGEXP = /[A-Z][a-zA-Z]*Error$/u
+
 // To mimic native error types and to print correctly with `util.inspect()`:
 //  - `error.name` should be assigned on the prototype, not on the instance
 //  - the constructor `name` must be set too
@@ -118,6 +122,7 @@ const setErrorName = function (ErrorType, name) {
   setNonEnumProp(ErrorType.prototype, 'name', name)
 }
 
+// Ensure those properties are not enumerable
 const setNonEnumProp = function (object, propName, value) {
   // eslint-disable-next-line fp/no-mutating-methods
   Object.defineProperty(object, propName, {