Using onerror
Letâs look at a few more constructs not available in PHP. Using
either the onerror
event or a
combination of the try
and catch
keywords, you can catch JavaScript errors
and deal with them yourself.
Events are actions that can be detected by
JavaScript. Every element on a web page has certain events that can
trigger JavaScript functions. For example, the onclick
event of a button element can be set to
call a function and make it run whenever a user clicks on the
button.
Example 14-11 illustrates
how to use the onerror
event.
<script> onerror = errorHandler document.writ("Welcome to this website") // Deliberate error function errorHandler(message, url, line) { out = "Sorry, an error was encountered.\n\n"; out += "Error: " + message + "\n"; out += "URL: " + url + "\n"; out += "Line: " + line + "\n\n"; out += "Click OK to continue.\n\n"; alert(out); return true; } </script>
The first line of this script tells the error event to use the new
errorHandler
function in the future.
This function takes three parametersâa message
, a url
, and a line
numberâand itâs a simple matter to display
all these in an alert pop-up.
Then, to test the new function, a syntax error is deliberately
placed in the code with a call to document.writ
instead of document.write
(the final e
is missing). Figure 14-1 shows the result of
running this script in a browser. Using onerror
this way can also be quite useful during the debugging process. ...
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