On Wednesday, July 11, 2012 10:23:55 AM UTC-7, Alex Tian wrote:
>
> Hello everyone,
>
> I am trying to test nodejs with mysql, I think due to its non-blocking
> nature. I have a difficult time to add the query result into a output
> buffer (var output in following code). Can anybody point me some way?
>
You seem to be missing one important concept. Callbacks don't interrupt
the currently executing function. In fact, they don't interrupt anything,
they'll wait until the current thread of execution (tick) is complete and
then run. Because of this, you can't reference the output of a callback
within the function (or even the tick) that sets up the callback.
Think of it this way. The V8 engine is going to execute your function in a
single tick. It's going to start at the top and work its way down,
following normal control flow. When you call a function that invokes a
callback (almost any function that *MAY* require I/O), that callback
doesn't happen until the I/O happens, so the engine continues processing
your function. So
output += '</body>\n</html>';
> res.end(output);
runs before any of the code in the callback, so that data hasn't been
appended to output at the time you send it with res.end();
The way to do this is to gather the data with the callbacks, and then
either output the data within the callbacks, or pass the data to a function
that will output the data.
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