2 files changed, 47 insertions, 0 deletions
diff --git a/date-fns/src/_lib/assign/index.js b/date-fns/src/_lib/assign/index.js
new file mode 100644
index 0000000..6fd8782
--- /dev/null
+++ b/date-fns/src/_lib/assign/index.js
@@ -0,0 +1,17 @@
+export default function assign(target, dirtyObject) {
+  if (target == null) {
+    throw new TypeError(
+      'assign requires that input parameter not be null or undefined'
+    )
+  }
+
+  dirtyObject = dirtyObject || {}
+
+  for (var property in dirtyObject) {
+    if (dirtyObject.hasOwnProperty(property)) {
+      target[property] = dirtyObject[property]
+    }
+  }
+
+  return target
+}
diff --git a/date-fns/src/_lib/assign/test.js b/date-fns/src/_lib/assign/test.js
new file mode 100644
index 0000000..629358f
--- /dev/null
+++ b/date-fns/src/_lib/assign/test.js
@@ -0,0 +1,30 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import assign from '.'
+
+describe('assign', function() {
+  it('assigns properties of the second argument to the first argument', function() {
+    var object = {}
+    assign(object, { a: 1, b: 2, c: 3 })
+    assert.deepEqual(object, { a: 1, b: 2, c: 3 })
+  })
+
+  it('the object passed as 2nd argument remains unchanged when the result is mutated', function() {
+    var object = { a: 1, b: 2, c: 3 }
+    var result = assign({}, object)
+    result.c = 4
+    assert.deepEqual(object, { a: 1, b: 2, c: 3 })
+  })
+
+  it('returns the first argument when the second argument is `undefined`', function() {
+    var original = { a: 1, b: 2, c: 3 }
+    var result = assign(original, undefined)
+    assert(original === result)
+  })
+
+  it('throws TypeError exception if the first argument is `undefined', function() {
+    assert.throws(assign.bind(null, undefined, { a: 1, b: 2, c: 3 }), TypeError)
+  })
+})