added keys-vs-values.js

Author: bahmutov

README.md

@@ -19,6 +19,7 @@ from [addyosmani/timing.js](https://github.com/addyosmani/timing.js).
 * [local-storage-size.js](local-storage-size.js) - measures size of the strings in the `localStorage`.
 * [expensive-keys.js](expensive-keys.js) - measures how much space individual keys and their values
 take up in a collection of objects, read [Measuring Space Allocation][measure].
+* [keys-vs-values.js](keys-vs-values.js) - measures length of keys vs length of values in an array.
 
 ### Angular performance
 

keys-vs-values.js

@@ -0,0 +1,60 @@
+// measures how much memory object keys take vs values in collection of objects
+(function keysVsValuesInit(root) {
+  function stringSize(str) {
+    // JavaScript strings are unicode UTF-16 up to 2 bytes per character
+    return str.length * 2;
+  }
+
+  function objectSize(obj) {
+    if (typeof obj === 'string') {
+      return stringSize(obj);
+    }
+    return stringSize(JSON.stringify(obj));
+  }
+
+  function values(obj) {
+    return Object.keys(obj).map(function (key) {
+      return obj[key];
+    });
+  }
+
+  function listSize(values) {
+    return values.reduce(function (total, value) {
+      return objectSize(value) + total;
+    }, 0);
+  }
+
+  function keysValues(obj) {
+    if (typeof obj === 'object') {
+      return {
+        keys: stringSize( Object.keys(obj).join('') ),
+        values: listSize( values(obj) )
+      };
+    } else {
+      return {
+        keys: 0,
+        values: objectSize(obj)
+      };
+    }
+  }
+
+  function keysVsValues(items) {
+    if (!Array.isArray(items) && typeof items === 'object') {
+      return keysVsValues([items]);
+    }
+
+    console.assert(Array.isArray(items));
+    return items.reduce(function (sizes, item) {
+      var size = keysValues(item);
+      sizes.keys += size.keys;
+      sizes.values += size.values;
+      return sizes;
+    }, {
+      keys: 0,
+      values: 0
+    });
+  }
+
+  root.keysVsValues = keysVsValues;
+  console.log('try keysVsValues(<array of objects>);');
+}(this));