Then name property can be used for such checks. But sometimes we have an error object coming from a 3rd-party library and there’s no easy way to get its class. We can use instanceof to check for particular errors.We just need to take care of the name property and don’t forget to call super. We can inherit from Error and other built-in error classes normally.It is widely used in object-oriented programming. The approach is called “wrapping exceptions”, because we take “low level” exceptions and “wrap” them into ReadError that is more abstract. No need to list all possible error types.
#Data toolbar javascript error code#
So the outer code checks instanceof ReadError and that’s it. In the code above, readUser works exactly as described – catches syntax and validation errors and throws ReadError errors instead (unknown errors are rethrown as usual). Original error: Synta圎rror: Unexpected token b in JSON at position 1
Throw new ReadError("Validation Error", err)
Throw new ReadError("Syntax Error", err) Here’s an example of how a valid json may look:Ĭlass PropertyRequiredError extends ValidationError Extending ErrorĪs an example, let’s consider a function readUser(json) that should read JSON with user data. For instance, HttpTimeoutError may inherit from HttpError, and so on. So it’s better to inherit from it.Īs the application grows, our own errors naturally form a hierarchy. But if we inherit, then it becomes possible to use obj instanceof Error to identify error objects. JavaScript allows to use throw with any argument, so technically our custom error classes don’t need to inherit from Error. HttpError objects may have a statusCode property with a value like 404 or 403 or 500. But they also may have other properties of their own, e.g. Our errors should support basic error properties like message, name and, preferably, stack. For errors in network operations we may need HttpError, for database operations DbError, for searching operations NotFoundError and so on. When we develop something, we often need our own error classes to reflect specific things that may go wrong in our tasks.
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