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readme.md
p-reduce
Reduce a list of values using promises into a promise for a value
Useful when you need to calculate some accumulated value based on async resources.
Install
$ npm install --save p-reduce
Usage
const pReduce = require('p-reduce');
const humanInfo = require('human-info'); // not a real module
const names = [
getUser('sindresorhus').then(info => info.name),
'Addy Osmani',
'Pascal Hartig',
'Stephen Sawchuk'
];
pReduce(names, (total, name) => {
return humanInfo(name).then(info => total + info.age);
}, 0).then(totalAge => {
console.log(totalAge);
//=> 125
});
API
pReduce(input, reducer, [initialValue])
Returns a Promise
that is fulfilled when all promises in input
and ones returned from reducer
are fulfilled, or rejects if any of the promises reject. The fulfilled value is the result of the reduction.
input
Type: Iterable<Promise|any>
Iterated over serially in the reducer
function.
reducer(previousValue, currentValue, index)
Type: Function
Expected to return a value. If a Promise
is returned, it's awaited before continuing with the next iteration.
initialValue
Type: any
Value to use as previousValue
in the first reducer
invocation.
Related
- p-each-series - Iterate over promises serially
- p-map-series - Map over promises serially
- p-map - Map over promises concurrently
- More…
License
MIT © Sindre Sorhus