出于某种原因,在下面的代码段中,构造函数委托似乎不起作用:
function NotImplementedError() {
Error.apply(this, arguments);
}
NotImplementedError.prototype = new Error();
var nie = new NotImplementedError("some message");
console.log("The message is: '"+nie.message+"'")
运行该命令得到的消息是:"。有什么想法,为什么,或者是否有更好的方法来创建一个新的错误子类?是否有一个问题,应用到本机错误构造函数,我不知道?
我也遇到过类似的问题。我的错误需要是error和NotImplemented的实例,它还需要在控制台中产生一致的回溯。
我的解决方案:
var NotImplemented = (function() {
var NotImplemented, err;
NotImplemented = (function() {
function NotImplemented(message) {
var err;
err = new Error(message);
err.name = "NotImplemented";
this.message = err.message;
if (err.stack) this.stack = err.stack;
}
return NotImplemented;
})();
err = new Error();
err.name = "NotImplemented";
NotImplemented.prototype = err;
return NotImplemented;
}).call(this);
// TEST:
console.log("instanceof Error: " + (new NotImplemented() instanceof Error));
console.log("instanceof NotImplemented: " + (new NotImplemented() instanceofNotImplemented));
console.log("message: "+(new NotImplemented('I was too busy').message));
throw new NotImplemented("just didn't feel like it");
使用node.js运行的结果:
instanceof Error: true
instanceof NotImplemented: true
message: I was too busy
/private/tmp/t.js:24
throw new NotImplemented("just didn't feel like it");
^
NotImplemented: just didn't feel like it
at Error.NotImplemented (/Users/colin/projects/gems/jax/t.js:6:13)
at Object.<anonymous> (/Users/colin/projects/gems/jax/t.js:24:7)
at Module._compile (module.js:449:26)
at Object.Module._extensions..js (module.js:467:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.runMain (module.js:487:10)
at process.startup.processNextTick.process._tickCallback (node.js:244:9)
该错误通过了我的所有3个标准,尽管stack属性是非标准的,但在大多数较新的浏览器中都支持它,这在我的情况下是可以接受的。
这部分的标准可以解释为什么错误。Apply调用不会初始化对象:
15.11.1错误构造函数作为函数调用
当Error作为函数而不是构造函数调用时,它会创建和
初始化一个新的Error对象。因此函数调用Error(…)是
等价于对象创建表达式new Error(…
相同的参数。
在这种情况下,Error函数可能确定它没有作为构造函数被调用,因此它返回一个新的Error实例,而不是初始化this对象。
用下面的代码进行测试似乎证明了这就是实际发生的情况:
function NotImplementedError() {
var returned = Error.apply(this, arguments);
console.log("returned.message = '" + returned.message + "'");
console.log("this.message = '" + this.message + "'");
}
NotImplementedError.prototype = new Error();
var nie = new NotImplementedError("some message");
运行此命令时输出如下:
returned.message = 'some message'
this.message = ''
这是我的实现:
class HttpError extends Error {
constructor(message, code = null, status = null, stack = null, name = null) {
super();
this.message = message;
this.status = 500;
this.name = name || this.constructor.name;
this.code = code || `E_${this.name.toUpperCase()}`;
this.stack = stack || null;
}
static fromObject(error) {
if (error instanceof HttpError) {
return error;
}
else {
const { message, code, status, stack } = error;
return new ServerError(message, code, status, stack, error.constructor.name);
}
}
expose() {
if (this instanceof ClientError) {
return { ...this };
}
else {
return {
name: this.name,
code: this.code,
status: this.status,
}
}
}
}
class ServerError extends HttpError {}
class ClientError extends HttpError { }
class IncorrectCredentials extends ClientError {
constructor(...args) {
super(...args);
this.status = 400;
}
}
class ResourceNotFound extends ClientError {
constructor(...args) {
super(...args);
this.status = 404;
}
}
示例用法#1:
app.use((req, res, next) => {
try {
invalidFunction();
}
catch (err) {
const error = HttpError.fromObject(err);
return res.status(error.status).send(error.expose());
}
});
示例用法#2:
router.post('/api/auth', async (req, res) => {
try {
const isLogged = await User.logIn(req.body.username, req.body.password);
if (!isLogged) {
throw new IncorrectCredentials('Incorrect username or password');
}
else {
return res.status(200).send({
token,
});
}
}
catch (err) {
const error = HttpError.fromObject(err);
return res.status(error.status).send(error.expose());
}
});
以下是Mozilla官方文档中的错误。
function NotImplementedError(message) {
var instance = new Error(message);
instance.name = 'NotImplementedError';
Object.setPrototypeOf(instance, Object.getPrototypeOf(this));
if (Error.captureStackTrace) {
Error.captureStackTrace(instance, NotImplementedError);
}
return instance;
}
NotImplementedError.prototype = Object.create(Error.prototype, {
constructor: {
value: Error,
enumerable: false,
writable: true,
configurable: true
}
});