diff --git a/747.largest-number-at-least-twice-of-others.js b/747.largest-number-at-least-twice-of-others.js
new file mode 100644
index 00000000..9622efca
--- /dev/null
+++ b/747.largest-number-at-least-twice-of-others.js
@@ -0,0 +1,18 @@
+/* URL of this problem
+ * https://leetcode.com/problems/largest-number-at-least-twice-of-others/description/
+ *
+ * @param {number[]} nums
+ * @return {number}
+ */
+
+var dominantIndex = function (nums) {
+  // Sort nums in a descending order
+  const SortedNums = [...nums].sort((a, b) => b - a);
+
+  if (SortedNums[0] / 2 >= SortedNums[1]) {
+    return nums.indexOf(SortedNums[0]);
+  }
+  return -1;
+};
+
+module.exports = dominantIndex;
diff --git a/dominantIndex.test.js b/dominantIndex.test.js
new file mode 100644
index 00000000..a2027d3d
--- /dev/null
+++ b/dominantIndex.test.js
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+const dominantIndex = require("./747.largest-number-at-least-twice-of-others");
+
+test("Return the index of the largest number in the array", () => {
+  expect(dominantIndex([3, 6, 1, 0])).toBe(1);
+});
+
+test("Return -1 if the largest integer is not at least twice as much as every other number in the array", () => {
+  expect(dominantIndex([1, 2, 3, 4])).toBe(-1);
+});
+
+test("Return -1 if the array is empty", () => {
+  expect(dominantIndex([])).toBe(-1);
+});
+
+test("Return -1 if the array is empty", () => {
+  expect(dominantIndex([])).toBe(-1);
+});
+
+test("Return the index of Infinity in the array if there is", () => {
+  expect(dominantIndex([3, 6, 1, 0, Infinity])).toBe(4);
+});
+
+test("Return the index of the largest number in the array with -Infinity", () => {
+  expect(dominantIndex([3, 6, 1, 0, -Infinity])).toBe(1);
+});