add noDisposeOnSet option

Close #70

README.md

@@ -66,6 +66,10 @@ away.
   `stale:true`, it'll return the stale value before deleting it.  If
   you don't set this, then it'll return `undefined` when you try to
   get a stale entry, as if it had already been deleted.
+* `noDisposeOnSet` By default, if you set a `dispose()` method, then
+  it'll be called whenever a `set()` operation overwrites an existing
+  key.  If you set this option, `dispose()` will only be called when a
+  key falls out of the cache, not when it is overwritten.
 
 ## API
 

lib/lru-cache.js

@@ -12,7 +12,6 @@ var Yallist = require('yallist')
 var symbols = {}
 var hasSymbol = typeof Symbol === 'function'
 var makeSymbol
-/* istanbul ignore if */
 if (hasSymbol) {
   makeSymbol = function (key) {
     return Symbol.for(key)
@@ -79,6 +78,7 @@ function LRUCache (options) {
   priv(this, 'allowStale', options.stale || false)
   priv(this, 'maxAge', options.maxAge || 0)
   priv(this, 'dispose', options.dispose)
+  priv(this, 'noDisposeOnSet', options.noDisposeOnSet || false)
   this.reset()
 }
 
@@ -314,8 +314,11 @@ LRUCache.prototype.set = function (key, value, maxAge) {
     var item = node.value
 
     // dispose of the old one before overwriting
+    // split out into 2 ifs for better coverage tracking
     if (priv(this, 'dispose')) {
-      priv(this, 'dispose').call(this, key, item.value)
+      if (!priv(this, 'noDisposeOnSet')) {
+        priv(this, 'dispose').call(this, key, item.value)
+      }
     }
 
     item.now = now

test/basic.js

@@ -300,6 +300,22 @@ test('disposal function', function (t) {
   t.end()
 })
 
+test('no dispose on set', function (t) {
+  var disposed = false
+  var cache = new LRU({
+    max: 1,
+    noDisposeOnSet: true,
+    dispose: function (k, n) {
+      disposed = n
+    }
+  })
+
+  cache.set(1, 1)
+  cache.set(1, 10)
+  t.equal(disposed, false)
+  t.end()
+})
+
 test('disposal function on too big of item', function (t) {
   var disposed = false
   var cache = new LRU({