diff --git a/README.md b/README.md
index 33a144e..1b3967e 100644
--- a/README.md
+++ b/README.md
@@ -37,8 +37,8 @@ $.ajax({
 
     cacheTTL: 1,           // Optional. In hours. Can be used with float to indicate part of an hour, e.g. 0.5.
     cacheKey: 'post',      // optional.
-    isCacheValid: function () {  // optional.
-        return true;
+    isCacheValid: function (data) {  // optional.
+        return data && data.code === '0';
     },
     isResponseValid: function (data, status, jqXHR) {  // optional.
         return data.code === '0';
diff --git a/jquery-ajax-localstorage-cache.js b/jquery-ajax-localstorage-cache.js
index 85d2350..88c5c86 100644
--- a/jquery-ajax-localstorage-cache.js
+++ b/jquery-ajax-localstorage-cache.js
@@ -83,13 +83,22 @@
             responseValid = options.isResponseValid,
             thenResponse = options.thenResponse || null,
             ttl,
+            dataType,
             value;
 
         if (!storage) return;
         ttl = storage.getItem(cacheKey + 'cachettl');
 
-        if (cacheValid && typeof cacheValid === 'function' && !cacheValid()){
+        value = storage.getItem(cacheKey);
+
+        if (value){
+            dataType = options.dataType || storage.getItem(cacheKey + 'dataType') || 'text';
+            if (dataType.toLowerCase().indexOf('json') !== -1) value = JSON.parse(value);
+        }
+
+        if (cacheValid && typeof cacheValid === 'function' && !cacheValid(value)){
             removeFromStorage(storage, cacheKey);
+            value = null;
             ttl = 0;
         }
 
@@ -98,7 +107,6 @@
             ttl = 0;
         }
 
-        value = storage.getItem(cacheKey);
         if (!value){
             // If value not in the cache, add a then block to request to store the results on success.
             jqXHR.then(thenResponse).then(function(data, status, jqXHR){