How To Create An Error Message In Javascript
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Sheppy evilpie Sevenspade Waldo Error.prototype.message In This Article DescriptionExamplesThrowing a custom errorSpecificationsBrowser compatibilitySee also The message property is a human-readable description of the error. Description This property contains a brief description of the error if one is available or has been set. SpiderMonkey makes extensive use of the message property for exceptions. The message property combined with the name property is used by node custom error the Error.prototype.toString() method to create a string representation of the Error. By default, the message property is an empty string, but this behavior can be overridden for an instance by specifying a message as the first argument to the Error constructor. Examples Throwing a custom error var e = new Error('Could not parse input'); // e.message is 'Could not parse input' throw e; Specifications Specification Status Comment ECMAScript 1st Edition (ECMA-262) Standard Initial definition. ECMAScript 5.1 (ECMA-262)The definition of 'Error.prototype.message' in that specification. Standard ECMAScript 2015 (6th Edition, ECMA-262)The definition of 'Error.prototype.message' in that specification. Standard ECMAScript 2017 Draft (ECMA-262)The definition of 'Error.prototype.message' in that specification. Draft Browser compatibility Desktop Mobile Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari Basic support (Yes) (Yes) (Yes) (Yes) (Yes) Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes) See also Error.prototype.name Error.prototype.toString() Document Tags and Contributors Tags: Error JavaScript Property Prototype Contributors to this page: fscholz, Mingun, Sheppy, evilpie, Sevenspade, Waldo Last updated by: fscholz, Dec 27, 2015, 7:15:57 AM See also Standard built-in objectsErrorPropertiesError.prototypeError.prototype.columnNumberError.prototype.fileNameError.prototype.lineNumberError.prototype.messageEr
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Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up How do I create a custom Error in JavaScript? up vote https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/message 133 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"); 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 http://stackoverflow.com/questions/783818/how-do-i-create-a-custom-error-in-javascript 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 14.8k1397123 asked Apr 23 '09 at 22:35 cdleary 27.3k40130178 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 Error types properly: github.com/fresheneesz/proto –B T Sep 10 '13 at 17:33 1 jsfiddle for a few of the top answers. –Nate Sep 22 '15 at 13:56 | show 1 more comment 16 Answers 16 active oldest votes up vote 126 down vote accepted Update your code to assign your prototype to the Error.prototype and the instanceof and your asserts work. function NotImplementedError(message) { this.name = "NotImplementedError"; th
the ability to create errors. My first reaction to the throw operator in Java was, "well that's stupid, why would you ever want to cause an error?" Errors were the enemy to me, something I sought to avoid, so the ability to cause an https://www.nczonline.net/blog/2009/03/03/the-art-of-throwing-javascript-errors/ error seemed like a useless and dangerous aspect of the language. I thought it was dumb to include the same operator in JavaScript, a language that people just didn't understand in the first place. Now with a great deal of experience under my belt, I'm a big fan of throwing my own errors. Doing so can lead to easier debugging and code maintenance when done properly. When programming, an error occurs when something unexpected happens. Maybe the incorrect value was custom error passed into a function or a mathematical operation had an invalid operand. Programming languages define a base set of rules that, when deviated from, result in errors so that the developer can fix the code. Debugging would be nearly impossible if errors weren't thrown and reported back to you. If everything failed silently, it would take you a long time to notice that there was an issue in the first place, let alone isolate and fix it. Errors are the friends javascript error message of developers, not enemies. The problem with errors is that they tend to pop up in unexpected places and at unexpected times. To make matters worse, the default error messages are usually too terse to really explain what went wrong. JavaScript error messages are notoriously uninformative and cryptic (especially in Internet Explorer), which only compounds the problem. Imagine if an error popped up with a message that said, "this function failed because this happened." Instantly, your debugging task becomes easier. This is the advantage of throwing your own errors. It helps to think of errors as built-in failure cases. It's always easier to plan for a failure at a particular point in code than it is to anticipate failure everywhere. This is a very common practice in product design, not just in code. Cars are built with crumple zones, areas of the frame that are designed to collapse in a predictable way when impacted. Knowing how the frame will react in a crash, which parts will fail, allow the manufacturers to ensure passenger safety. Your code can be constructed in the same way. Even though JavaScript has come a long way in the past few years, JavaScript developers still have far less tools to aid in debugging than developers of other languages. Throwing errors in your JavaScript is arguably more valuable than in any other language due to the difficulties around debugging. You can throw an by using the throw ope