Hi Dave,
The callback-based APIs follow a convention where the first positional
parameter is for error information. You're asking the Node 'fs' library to
read 'file1.txt'. If the read is successful, then the 2nd param ('data')
will contain a representation of the file's contents, and the 1st param
will be null. Alternatively, if an error occurs, then the err parameter
will have a value representing the error, and the 2nd param will be either
null or undefined.
The parameter names are a convention: you could call them 'apple' and
'orange', but that would really make your code hard to maintain!
Hope that helps,
Charles
On 26 November 2012 15:50, Dave Johnson <[email protected]> wrote:
> Hello and I apologise if this is a stupid question but I am reading up on
> Callbacks in node.js and wanted to ask something about it.
>
> Example code:
>
> fs.readFile('file1.txt', 'utf8', function (err, data) {
> if (err) throw err;
> console.log('File 1 read!');
> });
>
> I just dont know what the parameters *err* & *data* are, is this
> something that the node.js engine resolves internally? Hope I am making
> sense, in other coding you would create these variables and then pass them
> to a method.
>
> Thanks,
>
> Dave Johnson
>
>
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