Smoothing the promise map
I am wondering how you are going to flatten the results from a map of Promise promises that are arrays. I have a function that Promise.maps over a set of values, which themselves are promises (to be resolved) and return an array. So I am returning something like: [[1, 2, 3], [1, 2, 3], etc.] I used lodash / underscore._flatten after, however, I'm sure there is a cleaner method ...
return Promise.map(list, function(item) {
return new Promise(function(res, rej) {
return res([1, 2, 3]);
});
});
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1 answer
Not in bluebird flatMap
, you can .reduce
if you want to execute the results:
return Promise.map(list, function(item) {
return Promise.resolve([1, 2, 3]); // shorter than constructor
}).reduce(function(prev, cur){
return prev.concat(cur);
}, []);
Although lodash flatten will also work like:
return Promise.map(list, function(item) {
return Promise.resolve([1, 2, 3]); // shorter than constructor
}).then(_.flatten);
You can also teach bluebird to do this (if you are the author of the library - see how to get a new copy without collisions):
Promise.prototype.flatMap = function(mapper, options){
return this.then(function(val){
return Promise.map(mapper, options).then(_.flatten);
});
});
Promise.flatMap = function(val, mapper, options){
Promise.resolve(val).flatMap(mapper, options);
});
What would you do:
return Promise.flatMap(list, function(){
return Promise.resolve([1, 2, 3]);
});
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