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PromiseMap

Overview

PromiseMap attempts to take the ideas of Map and Promise and combine them into a useful tool for handling situations where you may be working with multiple promises simultaneously.

It does behave differently in a few aspects from Map.

  • Consuming (getting) values removes them from the Map once resolved.
  • Due to the above, we accept an array of keys to resolve / get
  • Values are resolved deeply if possible.
  • Values resolve until there are not any more promises. This means that if the promises continue to add to the same promise map it will never resolve itself since it will continually attempt to resolve the new promises until none remain (think of it like a short-lived event loop resolving to a value).

Installation

yarn add promise-map-es6

OR

npm install --save promise-map-es6

Simple Example

// assuming timeoutPromised() is:
const timeoutPromised = (fn, delay) =>
  new Promise((resolve, reject) => {
    setTimeout(() => {
      try {
        resolve(fn());
      } catch (e) {
        reject(e);
      }
    }, delay);
  });
export default timeoutPromised
import PromiseMap from 'promise-map-es6'
import timeoutPromised from './timeoutPromised'

const P = new PromiseMap()

P.set('foo', timeoutPromised(() => 1, 1000))
P.set('bar', timeoutPromised(() => 2, 2000))
P.set('baz', timeoutPromised(() => 3, 3000))

P.then(result => console.log(result))
// after 3 seconds: { foo: 1, bar: 2, baz: 3 }

PromiseMap Syntax

Note: All examples extend the example above by replacing the final function call.

  • PromiseMap.prototype.size
  • PromiseMap.prototype.length
  • PromiseMap.prototype.forEach()
  • PromiseMap.prototype.keys()
  • PromiseMap.prototype.get(...keys)
  • PromiseMap.prototype.set(key, promise)
  • PromiseMap.prototype.merge(promises)
  • PromiseMap.prototype.push(...promises)
  • PromiseMap.prototype.clear()
  • PromiseMap.prototype.has(...keys)
  • PromiseMap.prototype.entries(?...keys?)
  • PromiseMap.prototype.then(function (resolve, reject))
  • PromiseMap.prototype.catch()
  • PromiseMap[Symbol.iterator]

Prototype Properties

PromiseMap.prototype.size

Returns the number of key/value pairs in the PromiseMap object.

P.size; // 3

PromiseMap.prototype.length

Synonymous with PromiseMap.prototype.size

P.length; // 3

returns Number Map.size

Methods

PromiseMap.prototype.clear()

Removes all key/value pairs from the PromiseMap object. All promises are simply ignored without resolution since Promises are not cancellable by design.

P.size; // 3
P.clear();
P.size; // 0

returns undefined

PromiseMap.prototype.delete(...keys)

Deletes the given key(s) and returns the result for each. Each result is the result of running the delete method on the underlying Map.

P.size; // 3
P.delete('foo', 'baz'); // [true, true]
P.size; // 1

returns Array keys.map(k => Map.delete(k))

PromiseMap.prototype.entries(?...keys?)

Returns a Promise which resolves to a standard entries() result where each value is resolved. If keys is provided then only the given keys will be resolved. All resolved values are removed from the PromiseMap once consumed.

P.entries().then(entries => {
  console.log(entries); // [ ['foo', 1], ['bar', 2], ['baz', 3] ]
})
P.size; // 0
P.entries('foo', 'baz').then(entries => {
  console.log(entries); // [ ['foo', 1], ['baz', 3] ]
})
P.size; // 1

returns Promise .then(entries)

PromiseMap.prototype.get(...keys)

Returns a Promise which resolves with an object that represents the resolved key/value pairs that were requested. All resolved values are removed from the PromiseMap once consumed.

P.get('foo').then(result => console.log(result)); // { foo: 1 }
P.size; // 2

returns Promise .then(result)

PromiseMap.prototype.set(key, promise)

Sets a key on the PromiseMap. When the PromiseMap resolves, the resolved value of the promise will be available on that key of the object.

P.set('qux', timeoutPromised(() => 4, 3000)); // { foo: 1, bar: 2, baz: 3, qux: 4 }

returns PromiseMap

PromiseMap.prototype.merge(promises)

Takes a plain object of key/promise pairs and runs PromiseMap.set(key, promise) on each. Note that it is an error to set a key which already exists on the PromiseMap.

P.merge({
  qux: timeoutPromised(() => 4, 3000)
}).then(result => console.log(result)); // { foo: 1, bar: 2, baz: 3, qux: 4 }

returns PromiseMap

PromiseMap.prototype.has(...keys)

Returns Boolean whether all given keys are within the PromiseMap.

P.has('foo'); // true
P.has('foo', 'bar'); // true
P.has('foo', 'bar', 'blah'); // false

returns Boolean keys.every(k => Map.has(k))

PromiseMap.prototype.push(...promises)

Pushes new promises into the map. These promises will be resolved with the PromiseMap but their responses will not be added to the final object. This is useful if you want to make sure a given task is complete before resolving your final object, but don't want its resolved value to be included in the resulting object.

P.push(timeoutPromised(() => 4, 10000))

P.then(result => console.log(result))
// after 10 seconds: { foo: 1, bar: 2, baz: 3 }

returns undefined

PromiseMap.prototype.then(onResolve, onReject)

Resolves the entire PromiseMap and returns the result. PromiseMap will be empty once completed. Note that the second argument (onReject) is better handled by chaining a .catch().

In addition to resolving the promises within the PromiseMap, this will also resolve any Promises which are added to the PromiseMap during the resolution itself.

P.then(result => console.log(result)); // { foo: 1, bar: 2, baz: 3 }
P.size; // 0

returns Promise .then(result, error)

PromiseMap.prototype.catch(fn)

Resolves the entire PromiseMap and only registers a callback to occur should an error be caught while resolving the values. Note that since this consumes the values you will not be able to retrieve them when using this method.

P.add('errorExample', timeoutPromised(() => { throw new Error('Fail') }))
P.catch(e => console.log(e.name, e.message)); //  errorExample Fail
P.size; // 0

returns Promise