memoizeOne
A memoization library which only remembers the latest invocation
Rationale
Cache invalidation is hard:
There are only two hard things in Computer Science: cache invalidation and naming things.
Phil Karlton
So keep things simple and just use a cache size of one.
Unlike other memoization libraries, memoizeOne
only remembers the latest arguments and result. No need to worry about cache busting mechanisms such as maxAge
, maxSize
, exlusions
and so on which can be prone to memory leaks. memoizeOne
simply remembers the last arguments, and if the function is next called with the same arguments then it returns the previous result.
Usage
Standard usage
import memoizeOne from 'memoize-one';
const add = (a, b) => a + b;
const memoizedAdd = memoizeOne(add);
memoizedAdd(1, 2);
memoizedAdd(1, 2);
memoizedAdd(2, 3);
memoizedAdd(2, 3);
memoizedAdd(1, 2);
Play with this example
Custom equality function
You can also pass in a custom function for checking the equality of two items.
import memoizeOne from 'memoize-one';
import deepEqual from 'lodash.isEqual';
const identity = x => x;
const defaultMemoization = memoizeOne(identity);
const customMemoization = memoizeOne(identity, deepEqual);
const result1 = defaultMemoization({foo: 'bar'});
const result2 = defaultMemoization({foo: 'bar'});
result1 === result2
const result3 = customMemoization({foo: 'bar'});
const result4 = customMemoization({foo: 'bar'});
result3 === result4
Play with this example
Type signature
Here is the expected flow type signature for a custom equality function:
type EqualityFn = (a: any, b: any) => boolean;
Installation
yarn add memoize-one
npm install memoize-one --save
this
memoizeOne correctly respects this
control
This library takes special care to maintain, and allow control over the the this
context for both the original function being memoized as well as the returned memoized function. Both the original function and the memoized function's this
context respect all the this
controlling techniques:
- new bindings (
new
) - explicit binding (
call
, apply
, bind
); - implicit binding (call site:
obj.foo()
); - default binding (
window
or undefined
in strict mode
); - fat arrow binding (binding to lexical
this
) - ignored this (pass
null
as this
to explicit binding)
Changes to this
is considered an argument change
Changes to the running context (this
) of a function can result in the function returning a different value event though its arguments have stayed the same:
function getA() {
return this.a;
}
const temp1 = {
a: 20,
};
const temp2 = {
a: 30,
}
getA.call(temp1);
getA.call(temp2);
Therefore, in order to prevent against unexpected results, memoizeOne
takes into account the current execution context (this
) of the memoized function. If this
is different to the previous invocation then it is considered a change in argument. further discussion.
Generally this will be of no impact if you are not explicity controlling the this
context of functions you want to memoize with explicit binding or implicit binding. memoizeOne
will detect when you are manipulating this
and will then consider the this
context as an argument. If this
changes, it will re-execute the original function even if the arguments have not changed.
Code health