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Error Handling In Java
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to support the Lua project. Programming in Lua Part I. The Language Chapter 8. Compilation, Execution, and Errors 8.4 – Error Handling and Exceptions For many applications, you do not need to do any error handling in Lua. Usually, the application program does this handling. All Lua activities start from a call by the application, usually asking Lua to run a chunk. If there is any error, this call returns an error code and the application can take appropriate actions. In the case of the stand-alone interpreter, its main loop just prints https://no-errors.com/ the error message and continues showing the prompt and running the commands. If you need to handle errors in Lua, you should use the pcall function (protected call) to encapsulate your code. Suppose you want to run a piece of Lua code and to catch any error raised while running that code. Your first step is to encapsulate that piece of code in a function; https://www.lua.org/pil/8.4.html let us call it foo: function foo () ... if unexpected_condition then error() end ... print(a[i]) -- potential error: `a' may not be a table ... end Then, you call foo with pcall: if pcall(foo) then -- no errors while running `foo' ... else -- `foo' raised an error: take appropriate actions ... end Of course, you can call pcall with an anonymous function: if pcall(function () ... end) then ... else ... The pcall function calls its first argument in protected mode, so that it catches any errors while the function is running. If there are no errors, pcall returns true, plus any values returned by the call. Otherwise, it returns false, plus the error message. Despite its name, the error message does not have to be a string. Any Lua value that you pass to error will be returned by pcall: local status, err = pcall(function () error({code=121}) end) print(err.code) --> 121 These mechanisms provide all we need to do exception handling in Lua. We throw an exception with error and catch it with pcall. The error message identifies the kind or error. Copyright © 2003–2004 Roberto Ierusalimschy. All rights reserved.
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 Security best practices Performance best practices Resources https://expressjs.com/en/guide/error-handling.html TC Meetings Community Glossary 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). For example: app.use(function(err, req, res, next) { console.error(err.stack); res.status(500).send('Something broke!'); }); You define error-handling no error 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 any format that you prefer, such as an HTML error page, a simple message, or a JSON string. For organizational no error catcher (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 clientErrorHandler(err, req, res, next) { if (req.xhr) { res.status(500).send({ error: 'Something failed!' }); } else { next(err); } } The “catch-all” errorHandler function might be implemented as follows: function errorHandler(err, req, res, next) { res.status(500); res.render('error', { error: err }); }