'''`[https://tcl.tk/man/tcl/TclCmd/bgerror.htm%|%bgerror]`''' is the name of a
command that, if it exists, is invoked when an error occurs during the
evaluation of command under the [Tcl event loop].  `bgerror` was superceded in
[Changes in Tcl/Tk 8.5%|%Tcl 8.5] by [interp bgerror], but for the purpose of
backwards compatibility current versions of Tcl still support the `bgerror`
mechanism.



** Synopsis **

    :   '''bgerror''' ''message''



** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/bgerror.htm%|%man page%|%]:   



** Description **

"bgerror" is the name of the procedure that gets called to handle background
errors, i.e., errors that can not be propagated normally up the stack.

It is ''not'' expected that user code will call [[bgerror]] directly.  Instead,
it is there to be redefined so that user code can monitor and respond to errors
in event handlers.

    :   ''In very old code you may see this command written as `tkerror`; that name is obsolete nowadays. Use '''bgerror''' instead as it has the same semantics but without the implicit coupling to Tk.''



** Example **

During development, one might rush a hack like
======
proc bgerror message {
    puts stderr "An event-based script faulted with '$message'."
}
======
into use.

[DKF]: I find that it's better to print `[errorInfo]` in such cases.



** `bgerror` and [tile] in Tcl [Changes in Tcl/Tk 8.4%|%8.4]  **

[KPV] 2008-06-13 : In 8.4 the default bgerror code is not [tile] aware. Thus,
the following idiomatic (but incorrect) code will fail (more precisely, the
bgerror code configures a scrollbar's -relief which tile doesn't allow):
======
package require -exact Tk 8.4
package require tile
namespace import -force ::ttk::*
after 10 asdf
======

<<discussion>>

Does the documentation describe the calling convention?  I didn't notice
it.  My experience is that the error-handler invokes it as something like

======
bgerror [firstLineOf $::errorInfo]
======

----

[Ken]: I want to enquire what is the best method if i got a proc that runs
every 20s like the follow code but i want to catch its errors if any of the
proc that run afterwards run into errors? I heard using bgerror is not
recommended, so what is the best method?

======
proc a { } {
    #do something...
    after 1000 a 
}
======

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