code review: this fix broken pruning code for `domainCache`

src/js/uritools.js

@@ -289,8 +289,8 @@ URI.hostnameFromURI = function(uri) {
 
 URI.domainFromHostname = function(hostname) {
     // Try to skip looking up the PSL database
-    if ( domainCache.hasOwnProperty(hostname) ) {
     var entry = domainCache[hostname];
+    if ( entry !== undefined ) {
         entry.tstamp = Date.now();
         return entry.domain;
     }
@@ -316,6 +316,13 @@ var psl = publicSuffixList;
 // specific set of hostnames within a narrow time span -- in other words, I
 // believe probability of cache hit are high in uBlock.
 
+var domainCache = Object.create(null);
+var domainCacheCount = 0;
+var domainCacheCountLowWaterMark = 75;
+var domainCacheCountHighWaterMark = 100;
+var domainCacheEntryJunkyard = [];
+var domainCacheEntryJunkyardMax = domainCacheCountHighWaterMark - domainCacheCountLowWaterMark;
+
 var DomainCacheEntry = function(domain) {
     this.init(domain);
 };
@@ -328,7 +335,7 @@ DomainCacheEntry.prototype.init = function(domain) {
 
 DomainCacheEntry.prototype.dispose = function() {
     this.domain = '';
-    if ( domainCacheEntryJunkyard.length < 25 ) {
+    if ( domainCacheEntryJunkyard.length < domainCacheEntryJunkyardMax ) {
         domainCacheEntryJunkyard.push(this);
     }
 };
@@ -341,11 +348,10 @@ var domainCacheEntryFactory = function(domain) {
     return new DomainCacheEntry(domain);
 };
 
-var domainCacheEntryJunkyard = [];
-
 var domainCacheAdd = function(hostname, domain) {
-    if ( domainCache.hasOwnProperty(hostname) ) {
+    var entry = domainCache[hostname];
-        domainCache[hostname].tstamp = Date.now();
+    if ( entry !== undefined ) {
+        entry.tstamp = Date.now();
     } else {
         domainCache[hostname] = domainCacheEntryFactory(domain);
         domainCacheCount += 1;
@@ -357,7 +363,7 @@ var domainCacheAdd = function(hostname, domain) {
 };
 
 var domainCacheEntrySort = function(a, b) {
-    return b.tstamp - a.tstamp;
+    return domainCache[b].tstamp - domainCache[a].tstamp;
 };
 
 var domainCachePrune = function() {
@@ -375,15 +381,10 @@ var domainCachePrune = function() {
 };
 
 var domainCacheReset = function() {
-    domainCache = {};
+    domainCache = Object.create(null);
     domainCacheCount = 0;
 };
 
-var domainCache = {};
-var domainCacheCount = 0;
-var domainCacheCountLowWaterMark = 75;
-var domainCacheCountHighWaterMark = 100;
-
 psl.onChanged.addListener(domainCacheReset);
 
 /******************************************************************************/