Error Trapping Java Script
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中文 (简体) (zh-CN) Add a translation Edit Advanced Advanced History Print this article MDN Web technology For developers JavaScript JavaScript reference Statements and declarations try...catch Your Search Results samuele-artuso Markus Prokott http://www.w3schools.com/js/js_errors.asp fscholz valango SphinxKnight themitchy madarche Protron Noitidart Delapouite Havvy dezzadk indolering Sheppy trevorh Niggler secoif Dietrich Mgjbot Nanto vi Ptak82 Maian Nickolay Dria try...catch In This Article SyntaxDescriptionUnconditional catch clauseConditional catch clausesThe exception identifierThe finally clauseExamplesNested try-blocksReturning from a finally blockSpecificationsBrowser compatibilitySee also The try...catch statement marks a block of statements to try, and specifies a response, should an exception be thrown. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch Syntax try { try_statements } [catch (exception_var_1 if condition_1) { // non-standard catch_statements_1 }] ... [catch (exception_var_2) { catch_statements_2 }] [finally { finally_statements }] try_statements The statements to be executed. catch_statements_1, catch_statements_2 Statements that are executed if an exception is thrown in the try block. exception_var_1, exception_var_2 An identifier to hold an exception object for the associated catch clause. condition_1 A conditional expression. finally_statements Statements that are executed after the try statement completes. These statements execute regardless of whether or not an exception was thrown or caught. Description The try statement consists of a try block, which contains one or more statements ({} must always be used, also for single statements), and at least one catch clause or a finally clause, or both. That is, there are three forms of the try statement: try...catch try...finally try...catch...finally A catch clause contain statements that specify what to do if an exception is thrown in the try block. That is, you want the try block to succeed, and if it does not succeed, you want control to pass to the catch block. If any statement within
JavaScript, has been maturing since the dark ages of Netscape and IE4. No longer are you forced to settle for what the browser throws http://www.javascriptkit.com/javatutors/trycatch.shtml in your face in an event of a JavaScript error, but instead can take the matter into your own hands. The try/catch/finally statement of JavaScript lets you dip your toes into error prune territory and "reroute" when a JavaScript "exception" is encountered. Along with other defensive coding techniques such as Object detection error trapping and the onError event, try/catch/finally adds the ability to navigate around certain errors that in the past would have instantly stopped your script at its tracks. No more! try/catch/finally try/catch/finally are so called exception handling statements in JavaScript. An exception is an error that occurs at runtime due to an illegal operation during error trapping java execution. Examples of exceptions include trying to reference an undefined variable, or calling a non existent method. This versus syntax errors, which are errors that occur when there is a problem with your JavaScript syntax. Consider the following examples of syntax errors versus exceptions: alert("I am missing a closing parenthesis //syntax error alert(x) //exception assuming "x" isn't defined yet undefinedfunction() //exception try/catch/finally lets you deal with exceptions gracefully. It does not catch syntax errors, however (for those, you need to use the onerror event). Normally whenever the browser runs into an exception somewhere in a JavaScript code, it displays an error message to the user while aborting the execution of the remaining code. You can put a lid on this behaviour and handle the error the way you see fit using try/catch/finally. At its simplest you'd just use try/catch to try and run some code, and in the event of any exceptions, suppress them: try{ un