TapMap

The TapMap class extends JavaScript's native Map with a single, powerful method:

const map = new TapMap()
// "set the key 'foo' to 'bar' if 'foo' is not set"
map.tap('foo', 'bar')       // 'bar'
map.get('foo')              // 'bar'

// "set the key 'foo' to `Math.random()` if 'foo' is not set"
map.tap('foo', Math.random) // 'bar' (already set)
map.tap('bar', Math.random) // 0.3144890857392...

The default factory function returns a new TapMap, so you can use it to quickly build and then query deep structures:

const map = new TapMap()
map.tap(1).tap(2).tap(3, '!') // '!'
map.get(1).get(2)             // TapMap({3: '!'})

...or you can provide your own factory:

const map = new TapMap()
const values = ['foo', 'bar', 'foo', 'baz']
// it's better not to define this in the loop
const makeList = () => []
for (const [index, value] of Object.entries(values)) {
  map.tap(value, makeList).push(index)
}
for (const [value, indices] of map.entries()) {
  console.log(`${value}: ${indices.join(', ')}`)
}

Install

npm install tap-map

Usage

const TapMap = require('tap-map')
const map = new TapMap()
// do your worst