From c2588292cee15626d02bfde9498a27bcdd88e03d Mon Sep 17 00:00:00 2001
From: Jordan Eldredge <jordan@jordaneldredge.com>
Date: Mon, 1 Jan 2018 13:01:03 -0800
Subject: [PATCH] Add spliceIn utility function

---
 js/utils.js      |  6 ++++++
 js/utils.test.js | 16 +++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/js/utils.js b/js/utils.js
index 855843b6..4017b81e 100644
--- a/js/utils.js
+++ b/js/utils.js
@@ -187,3 +187,9 @@ export const filterObject = (obj, predicate) =>
     }
     return newObj;
   }, {});
+
+export const spliceIn = (original, start, newValues) => {
+  const newArr = [...original];
+  newArr.splice(start, 0, ...newValues);
+  return newArr;
+};
diff --git a/js/utils.test.js b/js/utils.test.js
index c519563e..a9c8792e 100644
--- a/js/utils.test.js
+++ b/js/utils.test.js
@@ -9,7 +9,8 @@ import {
   normalize,
   denormalize,
   segment,
-  moveSelected
+  moveSelected,
+  spliceIn
 } from "./utils";
 
 const fixture = filename =>
@@ -215,3 +216,16 @@ describe("moveSelected", () => {
     expect(moveSelected(arr, i => arr[i], -1)).toEqual([false, true, false]);
   });
 });
+
+describe("spliceIn", () => {
+  it("is immutable", () => {
+    const original = [1, 2, 3];
+    const spliced = spliceIn(original, 1, [200]);
+    expect(spliced).not.toBe(original);
+    expect(original).toEqual([1, 2, 3]);
+  });
+  it("adds values at the given index", () => {
+    const spliced = spliceIn([1, 2, 3], 1, [200]);
+    expect(spliced).toEqual([1, 200, 2, 3]);
+  });
+});