use built-in Node module - crypto

src/slack/slackInteraction.ts

@@ -2,6 +2,7 @@ import { ChatPostMessageArguments, ErrorCode } from "@slack/web-api";
 import { SlackWebClient } from "../helpers/types";
 import { getEmojisToReactWith } from "../emojis/emojiHandler";
 import SLACK_MESSAGE_BLOCKS from "../helpers/files/welcomeMessageBlocks.json";
+import { getRandomValue } from "../utils/getRandomValue";
 
 export async function addReactionToSlackPost(
     emoji: string,
@@ -121,8 +122,7 @@ export async function handleSlackJoinEvent(
     userId: string
 ): Promise<void> {
     const messages = SLACK_MESSAGE_BLOCKS.welcomeMessageBlocks;
-    const welcomeMessage =
-        messages[Math.floor(Math.random() * messages.length)];
+    const welcomeMessage = messages[getRandomValue({ range: messages.length })];
     // substitute user id in random welcome message with real user id
     const welcomeMessageText = welcomeMessage.blocks[0].text.text
         .split("@userId")

src/utils/getRandomValue.test.ts

@@ -0,0 +1,13 @@
+import { getRandomValue } from "./getRandomValue";
+
+describe("Get random value", () => {
+    it("should return random int value from 0-2 provided range 3", () => {
+        const randomValue = getRandomValue({ range: 3 });
+        expect([0, 1, 2].includes(randomValue)).toBe(true);
+    });
+
+    it("should return random int value from 0-4 provided range 5", () => {
+        const randomValue = getRandomValue({ range: 5 });
+        expect([0, 1, 2, 3, 4].includes(randomValue)).toBe(true);
+    });
+});

src/utils/getRandomValue.ts

@@ -0,0 +1,6 @@
+import crypto from "crypto";
+
+export const getRandomValue = ({ range }: { range: number }) => {
+    const array = new Uint32Array(1); // creates array with length only 1
+    return crypto.getRandomValues(array)[0] % range; //thus accessing first position in the array
+};