Add onEviction option (sindresorhus#20)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -4,6 +4,13 @@ declare namespace QuickLRU {
 		The maximum number of items before evicting the least recently used items.
 		*/
 		readonly maxSize: number;
+
+		/**
+		Called right before an item is evicted from the cache.
+
+		Useful for side effects or for items like object URLs that need explicit cleanup (`revokeObjectURL`).
+		*/
+		onEviction?: <KeyType, ValueType>(key: KeyType, value: ValueType) => void;
 	}
 }
 

index.js

@@ -7,6 +7,7 @@ class QuickLRU {
 		}
 
 		this.maxSize = options.maxSize;
+		this.onEviction = options.onEviction;
 		this.cache = new Map();
 		this.oldCache = new Map();
 		this._size = 0;
@@ -18,6 +19,13 @@ class QuickLRU {
 
 		if (this._size >= this.maxSize) {
 			this._size = 0;
+
+			if (typeof this.onEviction === 'function') {
+				for (const [key, value] of this.oldCache.entries()) {
+					this.onEviction(key, value);
+				}
+			}
+
 			this.oldCache = this.cache;
 			this.cache = new Map();
 		}

readme.md

@@ -45,6 +45,15 @@ Type: `number`
 
 The maximum number of items before evicting the least recently used items.
 
+#### onEviction
+
+*Optional*\
+Type: `(key, value) => void`
+
+Called right before an item is evicted from the cache.
+
+Useful for side effects or for items like object URLs that need explicit cleanup (`revokeObjectURL`).
+
 ### Instance
 
 The instance is [`iterable`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Iteration_protocols) so you can use it directly in a [`for…of`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/for...of) loop.

test.js

@@ -182,3 +182,24 @@ test('checks total cache size does not exceed `maxSize`', t => {
 	lru.get('1');
 	t.is(lru.oldCache.has('1'), false);
 });
+
+test('`onEviction` option method is called after `maxSize` is exceeded', t => {
+	const expectKey = '1';
+	const expectValue = 1;
+	let isCalled = false;
+	let actualKey;
+	let actualValue;
+
+	const onEviction = (key, value) => {
+		actualKey = key;
+		actualValue = value;
+		isCalled = true;
+	};
+
+	const lru = new QuickLRU({maxSize: 1, onEviction});
+	lru.set(expectKey, expectValue);
+	lru.set('2', 2);
+	t.is(actualKey, expectKey);
+	t.is(actualValue, expectValue);
+	t.true(isCalled);
+});