Creates a function that caches the last result of arguments, by key calculated from the arguments.
npm install memoize-last-for-key
npm install memoize-last-for-key --save
`
Creates a function that caches the last result of arguments, by key calculated from the arguments.
This library is useful if you can conclude a key from function's arguments where it is expected to receive the same arguments and return the same results.
See example below.
Info
The cache of the memoization function looks like this:
`
{
[generatedKeyFromArgs]: {
args: Array, // full args of the cached call
result: Any, // results for the cached call
entryOrder: Number // order of the cachedId
},
...
}
`
When a lastMemoized function is called:
1. we calculate it's key using keyResolver
1. if it doesn't exists in the cache, we calculate it's result and add it
1. old keys are deleted of their number exceeds size
1. if it exists exists we compare it's args to previous args using equalityFn
1. if the args are equal we return the cached result
1. otherwise we run the function and add the result to the cache
Example
`
const memoizeLast = require('memoize-last-for-key')
const config = {
keyResolver: function(args){
return args[0].id
}
}
const updateItemPrice = memoizeLast(function(item, newPrice){
// Some heavy calculation goes here.
// If it's not heavy, don't use this library.
return Object.assign({}, item, {price: newPrice})
}, config)
const item = {id: 1, name: 'item-1', price: 100}
const updatedItem = updateItemPrice(item, 200) //{id: 1, name: 'item-1', price: 200}
const anotherUpdatedItem = updateItemPrice(item, 200) //{id: 1, name: 'item-1', price: 200}
// updatedItem === anotherUpdatedItem
const newItem = {id: 1, name: 'item-2', price: 100}
const newUpdatedItem = updateItemPrice(newItem, 200) //{id: 1, price: 200}
// updatedItem !== newUpdatedItem because newItem is not item
`
Options
`
{
// Determines ow do we compare function's args to old args.
// If this function returns true, the result is pulled from the cache.
equalityFn: function defaultEqualityFn(oldArgs, newArgs){
return isDeepEqual(oldArgs, newArgs)
},
// The key we store and retrieve args and result from the cache.
// Upon retiraval we compare args to old args using equalityFn and decide if result should be recalculated.
keyResolver: function defaultKeyResolver(args){
return JSON.stringify(args[0])
},
// Number of keys in the hash table
length: 100,
// The this inside the memoize function
context: null
}
``