deep-memo

deep-memo

A memoize-one function that analyses the function output and retains previous object references wherever data hasn't changed.

Deep memo only caches the result of the most recent arguments. In addition to this, if the function is called with a different set of arguments, the result is analysed to identify parts of the returned data structure that haven't changed. For all parts of the data structure that haven't changed, deepMemo reuses the same objects and arrays from the last invocation. This allows strict equality check to be used downstream to tell if items have changed value or not.

Internally deepMemo uses fast-deep-equal for equality checking by value, and unmutable for the iteration and replace operations on the result.

Why?

If you need to perform many checks to work out if data has changed value, you might consider using a bunch of deep equality checks. But deep equality checks are expensive and generally require an external library. They also occur when data is read, rather than when data is written, and reads generally happen much more often than writes.

Memoizing deeply like deepMemo allows you to use fast strict equality checks to answer whether data has changed its value. The execution of deepMemo is a little more expensive to allow downstream equality checks to be fast and painless.

Example

import deepMemo from 'deep-memo';

let parseJson = (str) => JSON.parse(str);
let parseJsonMemoized = deepMemo(parseJson);

// call parseJsonMemoized

let firstCall = parseJsonMemoized(`{"foo":[1,2,3], "bar":[4,5,6]}`);

// calls parseJson and returns:
// {
//     foo: [1,2,3],
//     bar: [4,5,6]
// }

// call parseJsonMemoized again

let secondCall = parseJsonMemoized(`{"foo":[1,2,3], "bar":[4,5,6]}`);

// returns output from cache (fast!) and returns:
// {
//     foo: [1,2,3],
//     bar: [4,5,6]
// }

// call parseJsonMemoized with different nested data

let thirdCall = parseJsonMemoized(`{"foo":[1,2,3], "bar":[4,5,7]}`);

// calls parseJson and returns:
// {
//     foo: [1,2,3],
//     bar: [4,5,7]
// }

let hasFooChanged = secondCall.foo !== thirdCall.foo; // returns false
let hassBarChanged = secondCall.bar !== thirdCall.bar; // returns true

Packages

yarn add deep-memo