Guarantee isomorphism of flatten and unflatten commands

README.md

@@ -71,6 +71,7 @@ Use a custom delimiter for (un)flattening your objects, instead of `.`.
 When enabled, both `flat` and `unflatten` will preserve arrays and their
 contents. This is disabled by default.
 
+
 ``` javascript
 var flatten = require('flat')
 
@@ -158,3 +159,14 @@ flatten({
 //   'key3.a': { b: { c: 2 } }
 // }
 ```
+### shallow
+
+When enabled, nested flattened objects are preserved when unflattening.
+
+```
+unflatten({ "foo.bar": { "fiz.fuz": "hello" }})
+// { foo: { bar: { "fiz": { "fuz": "hello" } } }
+
+unflatten({ "foo.bar": { "fiz.fuz": "hello" }}, { shallow: true })
+// { foo: { bar: { "fiz.fuz": "hello" } }
+```

index.js

@@ -10,6 +10,8 @@ function flatten(target, opts) {
   var currentDepth = 1
   var output = {}
 
+  var changed = false
+
   function step(object, prev) {
     Object.keys(object).forEach(function(key) {
       var value = object[key]
@@ -34,19 +36,28 @@ function flatten(target, opts) {
         return step(value, newKey)
       }
 
+      if (newKey !== key) {
+        changed = true
+      }
+
       output[newKey] = value
     })
   }
 
   step(target)
 
-  return output
+  if (changed) {
+    return output
+  } else {
+    return target
+  }
 }
 
 function unflatten(target, opts) {
   opts = opts || {}
 
   var delimiter = opts.delimiter || '.'
+  var shallow = opts.shallow || false
   var overwrite = opts.overwrite || false
   var result = {}
 
@@ -55,6 +66,8 @@ function unflatten(target, opts) {
     return target
   }
 
+  var changed = false
+
   // safely ensure that the key is
   // an integer.
   function getkey(key) {
@@ -74,6 +87,8 @@ function unflatten(target, opts) {
     var recipient = result
 
     while (key2 !== undefined) {
+      changed = true
+
       var type = Object.prototype.toString.call(recipient[key1])
       var isobject = (
         type === "[object Object]" ||
@@ -94,11 +109,21 @@ function unflatten(target, opts) {
       }
     }
 
-    // unflatten again for 'messy objects'
-    recipient[key1] = unflatten(target[key], opts)
+    if (!shallow) {
+      // unflatten again for 'messy objects'
+      var value = target[key]
+      recipient[key1] = unflatten(target[key], opts)
+      changed = changed || value !== recipient[key1]
+    } else {
+      recipient[key1] = target[key]
+    }
   })
 
-  return result
+  if (changed) {
+    return result
+  } else {
+    return target
+  }
 }
 
 function isBuffer(value) {

test/test.js

@@ -12,6 +12,20 @@ var primitives = {
   , undefined: undefined
 }
 
+test('Isomorphism', function() {
+  var original = { foo: 'bar' }
+
+  assert.strictEqual(
+    original,
+    flatten(unflatten(original))
+  )
+
+  assert.strictEqual(
+    original,
+    unflatten(flatten(original))
+  )
+});
+
 suite('Flatten Primitives', function() {
   Object.keys(primitives).forEach(function(key) {
     var value = primitives[key]
@@ -115,6 +129,12 @@ suite('Flatten', function() {
     })
   })
 
+  test('Identity', function() {
+    var object = { foo: 'baz', fiz: 'fuz' }
+
+    assert.strictEqual(flatten(object), flatten(object))
+  })
+
   if (typeof Buffer !== 'undefined') test('Buffer', function() {
     assert.deepEqual(flatten({
       hello: {
@@ -263,6 +283,65 @@ suite('Unflatten', function() {
     }))
   })
 
+  test('Identity', function() {
+    var object = { foo: { bar: 'baz' } }
+
+    assert.strictEqual(unflatten(object), unflatten(object))
+  });
+
+  suite('.shallow', function() {
+    test('Should leave nested objects untouched', function() {
+      assert.deepEqual(unflatten({
+        'hello.world': { 'foo.fiz': 'bar' }
+      }, { shallow: true }), {
+        'hello': {
+          'world': {
+            'foo.fiz': 'bar'
+          }
+        }
+      })
+    });
+
+    test('Should preserve object identity', function() {
+      var object = {
+        'hello.world': { foo: 'bar' }
+      }
+
+      var unflattened1 = unflatten(object, { shallow: true })
+      var unflattened2 = unflatten(object, { shallow: true })
+
+      assert.deepEqual(unflattened1.hello.world, { foo: 'bar' })
+      assert.strictEqual(unflattened1.hello.world, unflattened2.hello.world)
+    })
+
+    test('Identity', function() {
+      var object = { foo: { "ir.re.le.vant": 'baz' } }
+
+      assert.strictEqual(
+        unflatten(object, { shallow: true }),
+        unflatten(object, { shallow: true })
+      )
+    });
+
+    test('Isomorphism 1', function() {
+      var object = { foo: { "ir.re.le.vant": 'baz' } }
+
+      assert.strictEqual(
+        object,
+        flatten(unflatten(object, { shallow: true }), { maxDepth: 1 })
+      )
+    });
+
+    test('Isomorphism 2', function() {
+      var object = { foo: { "ir.re.le.vant": 'baz' } }
+
+      assert.strictEqual(
+        object,
+        unflatten(flatten(object, { maxDepth: 1 }), { shallow: true })
+      )
+    });
+  })
+
   suite('.safe', function() {
     test('Should protect arrays when true', function() {
       assert.deepEqual(flatten({