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memoize.js
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69 lines (56 loc) · 1.53 KB
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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
// @flow
type Value = any;
type Key = any;
type Store = WeakMap<Key, Store | Value>;
function hasValue(keys: Key[], store: Store) {
let currentStore = store;
for (const key of keys) {
if (!currentStore || !currentStore.has(key)) {
return false;
}
currentStore = currentStore.get(key);
}
return true;
}
function getValue(keys: Key[], store: Store): Value {
let currentStore = store;
for (const key of keys) {
if (!currentStore) {
return null;
}
currentStore = currentStore.get(key);
}
return currentStore;
}
function setValue(keys: Key[], store: Store, value: Value) {
const keysExceptLast = keys.slice(0, -1);
const lastKey = keys[keys.length - 1];
let currentStore = store;
for (const key of keysExceptLast) {
if (!currentStore) {
return;
}
if (!currentStore.has(key)) {
currentStore.set(key, new WeakMap());
}
currentStore = currentStore.get(key);
}
if (currentStore) {
currentStore.set(lastKey, value);
}
}
// memoize with n arguments
export default function memoize(func: Function) {
const store = new WeakMap();
return function(...keys: Key[]) {
if (hasValue(keys, store)) {
return getValue(keys, store);
}
const newValue = func.apply(null, keys);
setValue(keys, store, newValue);
return newValue;
};
}