asalant · August 29, 2015 14:19 · Apr 23, 2015 · Apr 23, 2015 · Apr 23, 2015
diff --git a/output1 b/output1
@@ -15,4 +15,5 @@ No reviver: 179ms
 Regex reviver: 284ms
 Regex reviver optimized: 258ms
 
-So most of the time is spent actually converting the string to Date, not checking to see if it looks like a Date.
+So most of the time is spent actually converting the string to Date, not 
+checking to see if it looks like a Date.
diff --git a/output1 b/output1
@@ -2,9 +2,14 @@ No reviver: 148ms
 Regex reviver: 633ms
 Regex reviver optimized: 917ms
 
-Surprising to see that the additional length check in isIsoDateOptimized actually slows this down. The regex engine in node must be doing this kind of optimization already faster than JavaScript.
+Surprising to see that the additional length check in isIsoDateOptimized 
+actually slows this down. The regex engine in node must be doing this 
+kind of optimization already faster than JavaScript.
 
-Some of the time here is spent in new Date(). If we assume that consuming code of the parsed JSON would be doing that conversion of string to Date also, we should get rid of it in this test. Changing lines 16-17 to just `return value` results in the following:
+Some of the time here is spent in new Date(). If we assume that consuming 
+code of the parsed JSON would be doing that conversion of string to Date 
+also, we should get rid of it in this test. Changing lines 16-17 to just 
+`return value` results in the following:
 
 No reviver: 179ms
 Regex reviver: 284ms

diff --git a/date_reviver_perf.coffee b/date_reviver_perf.coffee
@@ -0,0 +1,38 @@
+isoDateRegex = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/
+
+isIsoDate = (value) ->
+  return value unless typeof(value) is 'string'
+
+  isoDateRegex.test(value)
+
+isIsoDateOptimized = (value) ->
+  return value unless typeof(value) is 'string'
+  return value unless value.length is 24
+
+  isoDateRegex.test(value)
+
+dateReviver = (dateTestFn) ->
+  (key, value) ->
+    return value unless dateTestFn(value)
+    return new Date(value)
+
+data = for i in [1..10000]
+  date1: new Date(Date.now() + i * 1000)
+  number: 1
+  string1: "Hello there"
+  string2: "Here's a slightly longer string."
+  obj: { a: 1, b: "2", c: '3'}
+
+json = JSON.stringify(data)
+
+startAt = Date.now()
+JSON.parse(json) for i in [1..10]
+console.log "No reviver: #{Date.now() - startAt}ms"#, parsed
+
+startAt = Date.now()
+JSON.parse(json, dateReviver(isIsoDate)) for i in [1..10]
+console.log "Regex reviver: #{Date.now() - startAt}ms"#, parsed
+
+startAt = Date.now()
+JSON.parse(json, dateReviver(isIsoDateOptimized)) for i in [1..10]
+console.log "Regex reviver optimized: #{Date.now() - startAt}ms"#, parsed
diff --git a/output1 b/output1
@@ -0,0 +1,13 @@
+No reviver: 148ms
+Regex reviver: 633ms
+Regex reviver optimized: 917ms
+
+Surprising to see that the additional length check in isIsoDateOptimized actually slows this down. The regex engine in node must be doing this kind of optimization already faster than JavaScript.
+
+Some of the time here is spent in new Date(). If we assume that consuming code of the parsed JSON would be doing that conversion of string to Date also, we should get rid of it in this test. Changing lines 16-17 to just `return value` results in the following:
+
+No reviver: 179ms
+Regex reviver: 284ms
+Regex reviver optimized: 258ms
+
+So most of the time is spent actually converting the string to Date, not checking to see if it looks like a Date.
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