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    An event handler for runtime script errors.

    Note that some/many error events do not trigger window.onerror, you have to listen for them specifically.


    window.onerror = funcRef;


    • funcRef is a reference to a function. When the function returns true, this prevents the firing of the default event handler. Function parameters:
      • Error message (string)
      • Url where error was raised (string)
      • Line number where error was raised (number)
      • Column number for the line where the error occurred (number) Requires Gecko 31.0
      • Error Object (object) Requires Gecko 31.0


    // Example 1:
    // Prevent error dialogs from displaying -which is the window's normal
    // behavior- by overriding the default event handler for error events that
    // go to the window.
    window.onerror = null;
    // Example 2:
    var gOldOnError = window.onerror;
    // Override previous handler.
    window.onerror = function myErrorHandler(errorMsg, url, lineNumber) {
      if (gOldOnError)
        // Call previous handler.
        return gOldOnError(errorMsg, url, lineNumber);
      // Just let default handler run.
      return false;


    The error event is raised when an error occurs in the script.

    When using the inline html markup (<body onerror="alert('an error occurred')>...), the arguments are not named. They can be referenced by arguments[0] through arguments[2].

    There is no Components.stack.caller to retrieve. (See bug 355430.)


    JavaScript 1.1

    Document Tags and Contributors

    Contributors to this page: Sheppy, teoli, Nickolay, Rappo, SergeG, Nux, Doekman, Delapouite, diegocr, kscarfone, MHasan
    Last updated by: teoli,
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