map-filter

When you need to run map and filter together (aka elegant reduce).

Why

I've seen code that looks like:

let list = [
  {name: 'alex', age: 28},
  {name: 'frank', age: 28},
  {name: 'joe', age: 30},
  {name: 'ayham', age: 28},
  {name: 'solomon', age: 29},
]

list.filter(p => p.age < 30).map(p => {name: p.name}) // youngsters!

Whereas you can achieve much better performance with a simple reduce:

list.reduce((acc, p) => {
  if (p.age < 30) {
    acc.push({name: p.name})
  }

  return acc
}, [])

No trust? Check yourself:

~/projects/js-map-filter (master ✔) ᐅ node bench.js                                                                                                                                                                                1s
filter + map: 19.378ms
reduce: 6.254ms
map-filter module: 7.116ms

So what does this guy do?

This utility lets you do the same things you'd do with a reduce, without having to keep track of the accumulator:

const mapFilter = require('map-filter')

filterMap(list, p => {
  if (p.age < 30) {
    return {name: p.name}
  }
})

Just return undefined (aka don't return) for the values you want to exclude from the final list.

Tests

Just mocha it:

~/projects/js-map-filter (master ✘)✹✭ ᐅ mocha                                                                                                                                                                                      1s


  mapFilter
    ✓ should be able to return all original values if no fn is specified
    ✓ should be able to exclude values
    ✓ should be able to map values
    ✓ should be able to handle falsey values


  4 passing (9ms)