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  • 5xxエラーの場合、出力にはHTTP仕様のステータスコードとステータス名のみが含まれます。
  • 4xxエラーの場合、出力には完全なエラーメッセージ(error.message)と、 検証の問題に関する、機械が読める詳細を提供するために通常使用されるdetails プロパティ(error.details)の内容が含まれます。 また出力には error.codeが含まれており、機械が読めるエラーコードを通過させることで、例えば翻訳に利用できます。

デバッグモードで strong-error-handler は、完全なエラースタックトレースと、HTTPレスポンスでクライアントにエラーオブジェクトの内部の詳細を返します。


$ npm install --save strong-error-handler



var express = require('express');
var errorHandler = require('strong-error-handler');

var app = express();
// setup your routes
// `options` are set to default values. For more info, see `options` below.
// app.use(errorHandler({ /* options, see below */ }));
  debug: app.get('env') === 'development',
  log: true,



  "final:after": {
    "strong-error-handler": {
      "params": {
         "debug": false,
         "log": true

一般に、strong-error-handler は一番最後のミドルウェア機能として登録されなければなりません。

上記の設定では、サーバーコンソールにエラーが記録されますが、HTTPレスポンスではスタックトレースは返されません。 設定オプションの詳細については、下記を参照してください。


strong-error-handler パッケージは JSON・HTML・XMLでのレスポンスをサポートしています。

  • When the object is a standard Error object, it returns the string provided by the stack property in HTML/text responses.
  • When the object is a non-Error object, it returns the result of util.inspect in HTML/text responses.
  • For JSON responses, the result is an object with all enumerable properties from the object in the response.

The content type of the response depends on the request’s Accepts header.

  • For Accepts header json or application/json, the response content type is JSON.
  • For Accepts header html or text/html, the response content type is HTML.
  • For Accepts header xml or text/xml, the response content type is XML.

There are plans to support other formats such as Plain-text.


Option Type Default Description
debug Boolean    false If true, HTTP responses include all error properties, including sensitive data such as file paths, URLs and stack traces. See Example output below.
log Boolean true If true, all errors are printed via console.error, including an array of fields (custom error properties) that are safe to include in response messages (both 4xx and 5xx).
If false, sends only the error back in the response.
safeFields [String] [] Specifies property names on errors that are allowed to be passed through in 4xx and 5xx responses. See Safe error fields below.
defaultType String "json" Specify the default response content type to use when the client does not provide any Accepts header.
negotiateContentType Boolean true Negotiate the response content type via Accepts request header. When disabled, strong-error-handler will always use the default content type when producing responses. Disabling content type negotiation is useful if you want to see JSON-formatted error responses in browsers, because browsers usually prefer HTML and XML over other content types.

Customizing log format


To use a different log format, add your own custom error-handling middleware then disable errorHandler.log. For example, in an Express application:

app.use(errorHandler({ log: false }));

In general, add strong-error-handler as the last middleware function, just before calling app.listen().


For LoopBack applications, put custom error-logging middleware in a separate file; for example, server/middleware/error-logger.js:

module.exports = function(options) {
  return function logError(err, req, res, next) {
    console.log('unhandled error' ,err);

Then in server/middleware.json, specify your custom error logging function as follows:

  // ...
  "final:after": {
    "./middleware/error-logger": {},
    "strong-error-handler": {
      "params": {
        "log": false

The default middleware.development.json file explicitly enables logging in strong-error-handler params, so you will need to change that file too.

Safe error fields

By default, strong-error-handler will only pass through the name, message and details properties of an error. Additional error properties may be allowed through on 4xx and 5xx status code errors using the safeFields option to pass in an array of safe field names:

  "final:after": {
    "strong-error-handler": {
      "params": {
        "safeFields": ["errorCode"]

Using the above configuration, an error containing an errorCode property will produce the following response:

  "error": {
    "statusCode": 500,
    "message": "Internal Server Error",
    "errorCode": "INTERNAL_SERVER_ERROR"

Migration from old LoopBack error handler

NOTE: This is only required for applications scaffolded with old versions of the slc loopback tool.

To migrate a LoopBack 2.x application to use strong-error-handler:

  1. In package.json dependencies, remove "errorhandler": "^x.x.x”,
  2. Install the new error handler by entering the command:
    npm install --save strong-error-handler
  3. In server/config.json, remove:
     "remoting": {
       "errorHandler": {
         "disableStackTrace": false

    and replace it with:

     "remoting": {
       "rest": {
         "handleErrors": false
  4. In server/middleware.json, remove:
     "final:after": {
       "loopback#errorHandler": {}

    and replace it with:

     "final:after": {
       "strong-error-handler": {}
  5. Delete server/middleware.production.json.
  6. Create server/middleware.development.json containing:
     "final:after": {
       "strong-error-handler": {
         "params": {
           "debug": true,
           "log": true


For more information, see Migrating apps to LoopBack 3.0.


5xx error generated when debug: false :

{ error: { statusCode: 500, message: 'Internal Server Error' } }

The same error generated when debug: true :

{ error:
  { statusCode: 500,
  name: 'Error',
  message: 'a test error message',
  stack: 'Error: a test error message    
  at Context.<anonymous> (User/strong-error-handler/test/handler.test.js:220:21)    
  at callFnAsync (User/strong-error-handler/node_modules/mocha/lib/runnable.js:349:8)    
  at (User/strong-error-handler/node_modules/mocha/lib/runnable.js:301:7)    
  at Runner.runTest (User/strong-error-handler/node_modules/mocha/lib/runner.js:422:10)    
  at User/strong-error-handler/node_modules/mocha/lib/runner.js:528:12    
  at next (User/strong-error-handler/node_modules/mocha/lib/runner.js:342:14)    
  at User/strong-error-handler/node_modules/mocha/lib/runner.js:352:7    
  at next (User/strong-error-handler/node_modules/mocha/lib/runner.js:284:14)    
  at Immediate._onImmediate (User/strong-error-handler/node_modules/mocha/lib/runner.js:320:5)    
  at tryOnImmediate (timers.js:543:15)    
  at processImmediate [as _immediateCallback] (timers.js:523:5)' }}

4xx error generated when debug: false :

{ error:
  { statusCode: 422,
  name: 'Unprocessable Entity',
  message: 'Missing required fields',