Yield the first async value returned for the co generator library.
This module is installed via npm:
$ npm install co-firstBy default, the co library only supports joining when ALL the asynchronous operations have returned:
var co = require('co');
co(function *() {
var a = yield asyncFunc1();
var b = yield asyncFunc1();
// wait for BOTH a and b to be returned
var res = yield [a, b];
})();But it is often useful to be able to just wait for only the FIRST value to be returned, for example, in the event of a timeout:
By default, co-first will return an object that contains both the
winning first async operation (on the caller property) and the value
on the value property, allowing you to do a switch after the
first to work out what happened:
var co = require('co'),
first = require('co-first');
co(function *() {
var a = yield asyncFunc1();
var b = yield asyncFunc1();
// wait for the FIRST of a and b to be returned
var firstResult = yield first([a, b]);
switch (firstResult.caller) {
case a:
var valA = firstResult.value;
break;
case b:
var valB = firstResult.value;
break;
}
})();When your asynchronous operations return the same value, then you can pass
true in for the last variable and just get the first value:
var co = require('co'),
first = require('co-first');
co(function *() {
var a = yield asyncFunc1();
var b = yield asyncFunc1();
// wait for the FIRST of a and b to be returned and simply return the
// winning value
var firstValue = yield first([a, b], true);
})();