Custom Error Handler Javascript
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Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, camel custom error handler helping each other. Join them; it only takes a minute: Sign up How do I create a custom Error in JavaScript? up vote 131 down vote favorite 56 For some reason it looks like constructor delegation doesn't work in the following snippet: function NotImplementedError() { Error.apply(this, arguments); } NotImplementedError.prototype = new Error(); var nie = new NotImplementedError("some message"); flask custom error handler console.log("The message is: '"+nie.message+"'") Running this gives The message is: ''. Any ideas as to why, or if there is a better way to create a new Error subclass? Is there a problem with applying to the native Error constructor that I don't know about? javascript exception share|improve this question edited Jul 26 '13 at 21:01 B T 14.7k1397123 asked Apr 23 '09 at 22:35 cdleary 27.3k40129178 Does nie instanceof NotImplementedError assertion work after your changes? I thought that in order for this to work you need to define NotImplementedError.prototype.constructor explicitly. –jayarjo Jul 9 '11 at 9:45 Next time, please tear out all the extraneous code that isn't required to demonstrate your issue. Also, wtc is js.jar ? Is that needed to reproduce the problem? –B T Jul 26 '13 at 20:39 1 Edited this question so that its understandable in 10 seconds rather than 10 minutes –B T Jul 26 '13 at 20:46 I created an inheritance/class library that inherits from Erro
I got a lot of responses and follow-up questions, so I thought I'd continue the discussion by explaining a little more
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about how to throw your own errors. To review, the basic syntax yii custom error handler is: throw new Error("message"); This works in all browsers and will display the error information in the same way
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it would any unintentional JavaScript error. The "message" string is stored in the message property of the object (which is what the browser uses to display the message). Periodically, I see http://stackoverflow.com/questions/783818/how-do-i-create-a-custom-error-in-javascript people throwing errors by just providing the string, such as this: throw "message"; Doing so will cause an error to be thrown, but not all browsers respond the way you'd expect. Firefox, Opera, and Chrome each display an "uncaught exception" message and then include the message string. Safari and Internet Explorer simply throw an "uncaught exception" error and don't provide the message https://www.nczonline.net/blog/2009/03/10/the-art-of-throwing-javascript-errors-part-2/ string at all. Clearly, this is suboptimal from a debugging point of view. Of course, you can throw any type of data that you'd like. There are no rules prohibiting specific data types: throw { name: "Nicholas" }; throw true; throw 12345; throw new Date(); The only thing to remember is that throwing any value will result in an error if it's not caught via a try-catch statement. Firefox, Opera, and Chrome all call String() on the value that was thrown to display something logical as the error message; Safari and Internet Explorer do not. The only surefire way to have all browsers display your custom error message is to use an Error object. ECMA-262, 3rd Edition actually specifies seven error object types. These are used by the JavaScript engine when various error conditions occur and can also be manually created: Error - base type for all errors. Never actually thrown by the engine. EvalError - thrown when an error occurs during execution of code via eval() RangeError - thrown when a number is outside the bounds of its range. For example, trying to
4 Moving to Express 5 Database integration API reference 4.x 3.x (deprecated) 2.x (deprecated) Advanced topics Template engines Using process managers Security updates https://expressjs.com/en/guide/error-handling.html Security best practices Performance best practices Resources TC Meetings Community Glossary https://www.sitepoint.com/exceptional-exception-handling-in-javascript/ Middleware Utility modules Frameworks Books and blogs Companies using Express Contributing to Express Release Change Log Error handling Define error-handling middleware functions in the same way as other middleware functions, except error-handling functions have four arguments instead of three: (err, req, res, next). custom error For example: app.use(function(err, req, res, next) { console.error(err.stack); res.status(500).send('Something broke!'); }); You define error-handling middleware last, after other app.use() and routes calls; for example: var bodyParser = require('body-parser'); var methodOverride = require('method-override'); app.use(bodyParser.urlencoded({ extended: true })); app.use(bodyParser.json()); app.use(methodOverride()); app.use(function(err, req, res, next) { // logic }); Responses from within a middleware function can be in custom error handler any format that you prefer, such as an HTML error page, a simple message, or a JSON string. For organizational (and higher-level framework) purposes, you can define several error-handling middleware functions, much like you would with regular middleware functions. For example, if you wanted to define an error-handler for requests made by using XHR, and those without, you might use the following commands: var bodyParser = require('body-parser'); var methodOverride = require('method-override'); app.use(bodyParser.urlencoded({ extended: true })); app.use(bodyParser.json()); app.use(methodOverride()); app.use(logErrors); app.use(clientErrorHandler); app.use(errorHandler); In this example, the generic logErrors might write request and error information to stderr, for example: function logErrors(err, req, res, next) { console.error(err.stack); next(err); } Also in this example, clientErrorHandler is defined as follows; in this case, the error is explicitly passed along to the next one. Notice that when not calling “next” in an error-handling function, you are responsible for writing (and ending) the response. Otherwise those requests will “hang” and will not be eligible for garbage collection. function clientErrorHandl
Web Dev @ Microsoft SEO By WooRank Books Courses Screencasts Newsletters Versioning Shop Forums Advertise Contribute Contact Us Our Story 995kSubscribers 132kFollowers 80kFollowers JavaScript Article Exceptional Exception Handling in JavaScript By Colin Ihrig May 31, 2012 Anything that can go wrong, will go wrong. Murphy's law is even applicable to software development. For non-trivial programs, it's not a matter of if, but when something will go wrong. Standards non-compliance, unsupported features, and browser quirks are just a few sources of potential problems facing web developers. Given all of the things that can go wrong, JavaScript has a surprisingly simple way of dealing with errors ― it just gives up and fails silently. At least, that's the behavior seen by the user. In reality, there is a lot going on under the hood. When a JavaScript statement generates an error, it is said to throw an exception. Instead of proceeding to the next statement, the JavaScript interpreter checks for exception handling code. If there is no exception handler, then the program returns from whatever function threw the exception. This is repeated for each function on the call stack until an exception handler is found or until the top level function is reached, causing the program to terminate. Error Objects When an exception occurs, an object representing the error is created and thrown. The JavaScript language defines seven types of built-in error objects. These error types are the foundation for exception handling. Each of the error types is described in detail below. Error The "Error" type is used to represent generic exceptions. This type of exception is most often used for implementing user defined exceptions. The topic of creating us