console.error.bind...?

[Anthony Kerz]

going thru the quick start, i see this:

db.on('error', console.error.bind(console, 'connection error:'));

i’m not familiar with that console.error.bind syntax, can someone set me straight?

regards,
tony.

[Jason Crawford]

The bind call is pretty fundamental to JavaScript; here's some documentation:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

Bottom line:

    console.error.bind(console, 'foo')

is basically equivalent to

    function () { console.error('foo'); }

But to fully understand why, it would help to read up on how functions work in JavaScript in general, especially different patterns of function invocation. Check out that documentation link above, and/or avail yourself of a reference like Crockford's book: http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742

Good luck,

Jason

--
Blog: http://blog.jasoncrawford.org  |  Twitter: @jasoncrawford

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[Anthony Kerz]

thanks jason,

now that you refreshed my memory, i’ve seen that core js bind() before.

i guess since:
(a) my head was in mongoose and
(b) every time i read about bind() my brain tucks it away in the “advanced stuff i won’t be using soon” junk drawer,
it didn’t click…

i should remember it now, at least to save my self some embarrassment ;)

then let me rephrase my original question to:

can anyone very briefly explain why we need to use bind() here:

db.on('error', console.error.bind(console, 'connection error:'));

like, could we have avoided bind() with something like:

db.on('error', function(err) { console.error('connection error: %s', err); })

?

[Jason Crawford]

Sure, you could do that. I would probably write it that way, personally. My guess is that whoever wrote the code decided that the shorter version was better.

-Jason