I have two functions that are asynchronous – they accept a function as a parameter which it called when it is done (callback).
function a(item, cb) {
someAsyncOperation(function () {
cb(item)
})
}
function b(item, cb) {
someAsyncOperation(function () {
cb(item)
})
}
I have an array. I need to run these functions, using Array.prototype.map, on this array two times. When both maps are done, I would like to have a callback which is invoked with two parameters: an error and the mapped array.
What sort of control flow do I need to achieve this? Something in the async library I'm guessing.
In pseudo-ish code:
var example = [1, 2, 3]
async.series([
function () { example.map(a) },
function () { example.map(b) }
], function (error, mappedExample) {
})
Yes, use the async library. It's awesome for doing this sort of thing.
If you need to do one map and then pass the results to the next function then you need to look at async.waterfall.
You can definitely use the async library for this sort of thing, but in this case, you can handle it yourself by simply chaining your functions together:
var items = ["a", "b", "c", "d" ],
foo = function (array, cb) {
"use strict";
array = array.map(function (element) {
return "foo-" + element;
});
cb(array);
},
baz = function (array) {
"use strict";
array = array.map(function (element) {
return "baz-" + element;
});
console.log(array);
};
foo(items, baz);
Results in:
[ 'baz-foo-a', 'baz-foo-b', 'baz-foo-c', 'baz-foo-d' ]
If your functions are particularly complex or you do this sort of thing often, then async can definitely be of help; however, there is no reason why can't do it on your own. (You would need to add error handling of course)