A memoization library which only remembers the latest invocation
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, memoize-one
only remembers the latest arguments and result. No need to worry about cache busting mechanisms such as maxAge
, maxSize
, exclusions
and so on which can be prone to memory leaks. memoize-one
simply remembers the last arguments, and if the function is next called with the same arguments then it returns the previous result.
import memoizeOne from 'memoize-one';
const add = (a, b) => a + b;
const memoizedAdd = memoizeOne(add);
memoizedAdd(1, 2); // 3
memoizedAdd(1, 2); // 3
// Add function is not executed: previous result is returned
memoizedAdd(2, 3); // 5
// Add function is called to get new value
memoizedAdd(2, 3); // 5
// Add function is not executed: previous result is returned
memoizedAdd(1, 2); // 3
// Add function is called to get new value.
// While this was previously cached,
// it is not the latest so the cached result is lost
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 // false - difference reference
const result3 = customMemoization({foo: 'bar'});
const result4 = customMemoization({foo: 'bar'});
result3 === result4 // true - arguments are deep equal
Here is the expected flow type signature for a custom equality function:
type EqualityFn = (a: any, b: any) => boolean;
# yarn
yarn add memoize-one
# npm
npm install memoize-one --save
import memoizeOne from 'memoize-one';
If you are in a CommonJS environment (eg Node), then you will need to add .default
to your import:
const memoizeOne = require('memoize-one').default;
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
orundefined
instrict mode
); - fat arrow binding (binding to lexical
this
) - ignored this (pass
null
asthis
to explicit binding)
Changes to the running context (this
) of a function can result in the function returning a different value even though its arguments have stayed the same:
function getA() {
return this.a;
}
const temp1 = {
a: 20,
};
const temp2 = {
a: 30,
}
getA.call(temp1); // 20
getA.call(temp2); // 30
Therefore, in order to prevent against unexpected results, memoize-one
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. memoize-One
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.
memoize-one
is super lightweight at 457 bytes
minified and 299 bytes
gzipped. (1kb
= 1000 bytes
)
memoize-one
performs better or on par with than other popular memoization libraries for the purpose of remembering the latest invocation.
Results
The comparisions are not exhaustive and are primiarly to show that memoize-one
accomplishes remembering the latest invocation really fast. The benchmarks do not take into account the differences in feature sets, library sizes, parse time, and so on.
- Tested with all built in JavaScript types.
- 100% code coverage
- Continuous integration to run tests and type checks.
Flow
types for safer internal execution and external consumption. Also allows for editor autocompletion.- Follows Semantic versioning (2.0) for safer consumption.
- No dependencies