javascript 在Node.js中创建自定义错误类

Posted 2021-05-04

// Mini test suite for our custom error

var assert = require('assert');
var CustomError = require('./errors/custom-error');

function doSomethingBad() {
  throw new CustomError('It went bad!', 42);
}

try {
  doSomethingBad();
} catch (err) {
  // The name property should be set to the error's name
  assert(err.name = 'CustomError');

  // The error should be an instance of its class
  assert(err instanceof CustomError);

  // The error should be an instance of builtin Error
  assert(err instanceof Error);

  // The error should be recognized by Node.js' util#isError
  assert(require('util').isError(err));

  // The error should have recorded a stack
  assert(err.stack);

  // toString should return the default error message formatting
  assert.strictEqual(err.toString(),
                     'CustomError: It went bad!');

  // The stack should start with the default error message formatting
  assert.strictEqual(err.stack.split('\n')[0],
                     'CustomError: It went bad!');

  // The first stack frame should be the function where the error was thrown.
  assert.strictEqual(err.stack.split('\n')[1].indexOf('doSomethingBad'), 7);

  // The extra property should have been set
  assert.strictEqual(err.extra, 42);
}

// Spoiler: It passes!

It's nice to be able to distinguish error types by classes. But it's a bit tricky to correctly create a custom error class in Node.js, so here is an example.

The example also shows how to add an extra parameter called `extra` that will be stored as a property on the error.

### Usage

``` js
var CustomError = require('./errors/custom-error');

function doSomethingBad() {
  throw new CustomError('It went bad!', 42);
}
```

### Features

* **Name appears once** - less editing if you have to create lots of custom error classes
* **Easy to subclass** - just change the last line to inherit from another custom error class you created
* **Correct stack trace** - no extra stack frames, no double capturing of the stack trace

### Anti-patterns

These are some things that I've seen in other proposed solutions that you should avoid.

* `Error.call(this)` - creates another error object (wasting a bunch of time) and doesn't touch `this` at all
* `Error.captureStackTrace(this, arguments.callee);` - works, but `arguments.callee` is deprecated, so don't use it
* `this.stack = (new Error).stack` - this... I don't even...

'use strict';

module.exports = function CustomError(message, extra) {
  Error.captureStackTrace(this, this.constructor);
  this.name = this.constructor.name;
  this.message = message;
  this.extra = extra;
};

require('util').inherits(module.exports, Error);