These statements execute regardless of whether an exception was thrown or caught. In the following example, code in the try block can potentially throw three exceptions: , , and. Returning from a finally block If the finally block returns a value, this value becomes the return value of the entire try-catch-finally production, regardless of any return statements in the try and catch blocks. In Firefox 58, when the exception is unused, the identifier can be omitted, as in the code below. This includes exceptions thrown inside of the catch block: function { try { try throw new Error 'oops' ; catch ex { console. must always be used, even for single statements. Conditional catch clauses Non-standard This feature is non-standard and is not on a standards track. See the for more information on JavaScript exceptions. Not for use in new websites. If an inner try statement does not have a catch clause, the enclosing try statement's catch clause is entered.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone and send us a pull request. These statements execute regardless of whether an exception was thrown or caught. Description The try statement consists of a try javascript try catch, which contains one or more statements. must always be used, even for single statements. At least one catch clause, or a finally clause, must be present. That is, you want the try block to succeed, and if it does not succeed, you want to pass control to the catch block. If any statement within the try block or in a function called from within the try block throws an exception, control is immediately shifted to the catch clause. If no exception is thrown in the try block, the catch clause is skipped. The finally clause executes after the try block and catch clause s execute but before the statements following the try statement. It always executes, regardless of whether an exception was thrown or caught. You can nest one or more try statements. If an inner try statement does not have a catch clause, the enclosing try statement's catch clause is entered. You can also use the try statement to handle JavaScript exceptions. See the for more information on JavaScript exceptions. Unconditional catch clause When a single, unconditional catch clause is used, the catch block is entered when any exception is thrown. For example, when the exception occurs in the following code, control transfers to the catch clause. The catch block is unique in that JavaScript creates this identifier when the catch block is entered, and it adds it to the current scope; the identifier lasts only for the duration of the catch block; after the catch block finishes executing, the identifier is no longer available. Conditional catch clauses Non-standard This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future. You can also use one or more conditional javascript try catch clauses to handle specific exceptions. In this case, the appropriate catch clause is entered when the specified exception is thrown. In the following example, code in the try block can potentially throw three exceptions:, and. When an exception occurs, control transfers to the appropriate catch clause. If the exception is not one of the specified exceptions and an unconditional catch clause is found, control transfers to that catch clause. If you use an unconditional catch clause with one or more conditional catch clauses, the unconditional catch clause must be specified last. Otherwise, the unconditional catch clause will intercept all types of exception before they can reach the conditional ones. It's not supported in any current browser anymore. You can use this identifier to get information about the exception that was thrown. This identifier is local to the catch clause. That is, it is created when the catch clause is entered, and after the catch clause finishes executing, the identifier is no longer available. In Firefox 58, when the exception is unused, the identifier can be omitted, as in the code below. This is also and later. Note that the finally clause executes regardless of whether an exception is thrown. Also, if an exception is thrown, the statements in the finally clause execute even if no catch clause handles the exception. You can use the finally clause to make your script fail gracefully when an exception occurs; for example, to do general cleanup, you may need to release a resource that your script has tied javascript try catch. It may seem strange to have a special exception-related clause that executes regardless of whether there is an exception, but this construct actually does serve a purpose. The important point is not that the finally-clause always executes, but rather that ordinary code following a try. For instance, javascript try catch another exception occurs inside a try's catch-block, any remaining code in the same outer try-block enclosing that try. Thus, any routine cleanup code done in that enclosed or the main section before it exits, will be skipped. Now, if that routine cleanup must be done whether or not the try. The following example opens a file and then executes statements that use the file server-side JavaScript allows you to access files. If an exception is thrown while the file is open, the finally clause closes the file before the script fails. The code in finally also executes upon explicitly returning from try or catch block. Returning from a finally block If the finally block returns a value, this value becomes the return value of the entire try-catch-finally production, regardless of any return statements in the try and catch blocks. This includes exceptions thrown inside of the catch block: function { try { try javascript try catch new Error 'oops' ; catch ex { console. The same would apply to any value returned from the catch block. Specifications Specification Status Comment Standard Initial definition. Not for use in new websites. Not for use in new websites.
