key-master
v4.1.0
Published
hashmap + constructor function = a hashmap you don't have to check before calling get()
Downloads
1,705
Readme
key-master
Replaces "maintain a map of constructed objects" boilerplate.
Seen this pattern before?
const defaultValue = key => [ key ]
const myMap = new Map()
// ...
function doStuff(thing) {
if (!myMap.has(thing)) {
myMap.set(thing, defaultValue(thing))
}
actuallyDoStuff(myMap.get(thing))
}
I figure I've typed that enough times in my life. Now I'm going to just use this module.
const map = keyMaster(key => defaultValue(key))
map.get('howdy') // => [ 'howdy' ]
actuallyDoStuff(map.get('howdy'))
Usage
- Install:
npm install key-master
- Use:
const keyMaster = require('key-master')
This library uses ES2015 syntax, so if you're deploying to IE11, you'll need to be transpiling your project with Babel or something.
API
const map = keyMaster(defaultValueReturningFunction, [map])
The defaultValueReturningFunction
is called whenever the map doesn't already have a value for the given key.
It is passed the key as its first argument.
The map
argument is optional. It can be anything implementing .get
, .set
, .has
, and .delete
. If not passed in, keyMaster
will use a new JavaScript Map by default.
const map = keyMaster(yourFactory)
const map = keyMaster(yourFactory, new WeakMap())
const map = keyMaster(yourFactory, new Map())
const map = keyMaster(yourFactory, { get, set, has, delete })
value = map.get(key)
Returns the value in the map. If there isn't a value for that key, the constructor calls the defaultValueReturningFunction
that was passed to the constructor, passing in the key. Whatever the constructor function returns is inserted into the map and returned by get
.
map.set(key, value)
Inserts a value into the map, overwriting anything that might be there.
map.delete(key)
Removes a value from the map.
bool = map.has(key)
Returns true
if the key exists in the map, false
if the key does not exist in the map.
jsMap = map.getUnderlyingDataStructure()
Returns the underlying data structure. If you passed in a map to the constructor, it returns that. Otherwise, it returns the plain-old object that was used as a hashmap.
Using a plain-old-object as a map
If you want to use an object as a map instead of a Map
or WeakMap
, you can use this function to create a map to pass in:
function makeObjectMap() {
var obj = Object.create(null)
return {
get: function(key) {
return obj[key]
},
set: function(key, value) {
obj[key] = value
},
has: function(key) {
return Object.prototype.hasOwnProperty.call(obj, key)
},
delete: function(key) {
delete obj[key]
},
object: obj
}
}