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JAVASCRIPT

JavaScript Errors
By: James Payne
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  • Rating: 4 stars4 stars4 stars4 stars4 stars / 7
    2008-01-07

    Table of Contents:
  • JavaScript Errors
  • Try...Catch
  • Throwing the Ball (and Exceptions)
  • By the Numbers

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    JavaScript Errors - Throwing the Ball (and Exceptions)


    (Page 3 of 4 )

    The Throw statement allows you to create an exception. This is useful when trying to generate informative error messages.

    Let's say you wanted to create a program that asked a user a question when the page first loaded. If they answer it right, they get to view the page; if not something else happens to them. Here it is in code:


    <html>

    <body>

    <script type="text/javascript">

    var name=prompt("Enter your name:","")

    try

    {

    if(name == "James")

    throw "FirstError"

    else if(name == "Houston")

    throw "SecondError"

    else if(isNaN(name))

    throw "ThirdError"

    }

    catch(er)

    {

    if(er=="FirstError")

    alert("Alert! Alert! James is too heavy for the page to load!")

    if(er == "SecondError")

    alert("Alert! Alert! You may not haxor our bases!")

    if(er == "ThirdError")

    alert("Greetings...we've been expecting you.")

    }

    </script>

    </body>

    </html>

    This code displays a prompt asking for the user's name. Depending on the name entered, a different message will occur prior to the page loading. If the user types in James, it throws the FirstError exception, and the following alert box will appear:




    If the user types in Houston, it triggers the SecondError exception, and this alert is displayed:




    And lastly, if the user enter anything else (even if they type in james in lowercase), the ThirdError exception is triggered and this alert will appear:



    Note that the word throw must be written in lowercase or you will receive Javascript errors, which of course is what we are trying to avoid.

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