Javascript Catching Syntax Error
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Potappo Sevenspade SyntaxError In This Article DescriptionSyntaxParametersPropertiesMethodsSyntaxError instancesPropertiesMethodsExamplesCatching a SyntaxErrorCreating a SyntaxErrorSpecificationsBrowser compatibilitySee also The SyntaxError object represents an error when trying to interpret syntactically invalid code. Description A SyntaxError is thrown when the JavaScript engine encounters tokens or token order that does not conform to the syntax of the language when parsing code. Syntax new SyntaxError([message[, fileName[, lineNumber]]]) Parameters message Optional. Human-readable description of the error fileName Optional. The name of the file containing the code that caused the exception lineNumber Optional. The line number of the code that caused the exception Properties SyntaxError.prototype Allows the addition of properties to a SyntaxError object. Methods The global SyntaxError contains no methods of its own, however, it does inherit some methods through the prototype chain. SyntaxError instances Properties SyntaxError.prototype
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JavaScript, has been maturing since the dark ages of Netscape and IE4. No longer are you forced to settle for what the browser throws 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 http://www.javascriptkit.com/javatutors/trycatch.shtml 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 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 syntax error due to an illegal operation during 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 javascript catching syntax 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{ undefinedfunction() } catch(e){ //catch and just suppress error } Assuming undefinedfunction() is undefined, when the browser runs the above, no errors will be shown. The syntax for try/catch/finally is a try clause followed by either a catch or finally clause (at least one or both of them). The catch clause if defined traps any errors that has occurred from try, and is indirectly passed the error object that contains additional info about the error. Lets see a slightly more complex example now: try{ undefinedfunction() alert('I guess you do exist') } catch(e){ alert('An error has occurred: '+e.message) } Demo: Click on the above button, and notice how only "An Error has occurred" alert pops up, but not "I guess you do exist". This tells us that when try encounters an error, it immediately skips any remaining code inside it and goes s