为什么thunkify / yield总是返回一个数组？

Question

I have a thunk called logInline (adapted from the Co documentation ).

I notice the thunkified get always seems to yield an array. Is this by design? Is it thunkify doing this, or is it a standard part of yield ?

var co = require('co'),
  get = thunkify(request.get);

var logInline = co(function *(){
  var google = yield get('http://google.com'); 
  console.log(google[0].statusCode);
})

logInline()

Note the variable 'google' here is always an array. Why? Note that request.get normally returns err, response (ie, there are no arrays).

The script, BTW, returns 200 or whatever other response code google.com returns.

Alas the yield documentation is pretty sparse ATM.

Edit: Thunks don't always return arrays. Eg if var readFile = thunkify(fs.readFile); :

var fileContents = yield readFile('myfile', 'utf8');
log(fileContents);

In this case, fileContents is not returned inside an array. So why was google inside an array? There seems to be something in thunkify controlling what the thunks return

Answer 1

I notice the thunkified get always seems to yield an array. Is this by design?

I don't know and cannot confirm, as you say the docs (of co, yield is not of interest here) are quite sparse.

I could however image that the yield does result in the arguments-array of the callback, to easily support multiple return values. You might use a destructuring assignment to get the single results back:

co(function *(){
  var [google] = yield get('http://google.com'); 
  console.log(google.statusCode);
})

---

Edit:

There seems to be something in thunkify controlling what the thunks return

Indeed, this happens only sometimes. I now checked the code , which reads

if (arguments.length > 2) res = slice.call(arguments, 1);

so if the callback function (of the thunkified call, but imagine it to be the one that is passed to fs.readFile or request.get directly) is called with more than one result argument (the error parameter is ignored), then an array will be yield ed to your generator code.