Add possibility to use function as the second argument

lib/intersperse.js

@@ -1,11 +1,12 @@
 module.exports = intersperse;
 
-function intersperse(arr, obj) {
+function intersperse(arr, value) {
 	if (!arr.length) return [];
 	if (arr.length === 1) return arr.slice(0);
 
 	var items = [arr[0]];
 	for (var i = 1, len = arr.length; i < len; ++i) {
+		var obj = typeof value === 'function' ? value(arr[i - 1], arr[i], i) : value;
 		items.push(obj, arr[i]);
 	}
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "intersperse",
-  "version": "1.0.0",
+  "version": "1.1.0",
   "description": "Add an object to an array between each element",
   "main": "lib/intersperse.js",
   "directories": {

test/test.js

@@ -27,4 +27,23 @@ describe('intersperse', function () {
 		assert.deepEqual(newArr, [1, 'a', 2, 'a', 3]);
 		assert.deepEqual(arr, [1, 2, 3]);
 	});
-});
+
+	it("should accept function as a parameter", function () {
+		var arr = [1, 2, 3];
+		var newArr = intersperse(arr, function() {
+			return 'a';
+		});
+
+		assert.deepEqual(newArr, [1, 'a', 2, 'a', 3]);
+		assert.deepEqual(arr, [1, 2, 3]);
+	});
+
+	it("should input previous, next and index values for function", function () {
+		var arr = [1, 2];
+		var newArr = intersperse(arr, function(prev, next, i) {
+			assert.equal(prev, 1);
+			assert.equal(next, 2);
+			assert.equal(i, 1);
+		});
+	});
+});