commitlint: introduce TypeHelpers.IsInstanceOf

The keyword `instanceof` is a footgun in JS/TS because it
only works for classes, but not primitive types.

This was taken from:
https://stackoverflow.com/a/58184883/544947

commitlint/fpHelpers.ts

@@ -49,3 +49,16 @@ export class OptionStatic {
         }
     }
 }
+
+export class TypeHelpers {
+    // because instanceof doesn't work with primitive types (e.g. String), taken from https://stackoverflow.com/a/58184883/544947
+    public static IsInstanceOf(variable: any, type: any) {
+        let res: boolean = false;
+        if (typeof type == "string") {
+            res = typeof variable == type.toLowerCase();
+        } else {
+            res = variable.constructor == type;
+        }
+        return res;
+    }
+}

commitlint/tests/testHelpers.ts

@@ -1,5 +1,5 @@
 import { test, expect } from "vitest";
-import { None, Some, Option, OptionStatic } from "../fpHelpers.js";
+import { None, Some, Option, OptionStatic, TypeHelpers } from "../fpHelpers.js";
 const { spawnSync } = require("child_process");
 const os = require("os");
 
@@ -50,6 +50,45 @@ test("testing OfObj", () => {
     expect(typeGuard(ofObj2(four))).toBe("NAH");
 });
 
+class Foo {
+    public JustToMakeFooNonEmpty() {
+        return null;
+    }
+}
+class Bar {
+    public JustToMakeBarNonEmpty() {
+        return null;
+    }
+}
+
+test("testing TypeHelpers.IsInstanceOf", () => {
+    let str1 = "foo";
+    expect(TypeHelpers.IsInstanceOf(str1, String)).toBe(true);
+    let str2 = String("foo");
+    expect(TypeHelpers.IsInstanceOf(str2, String)).toBe(true);
+
+    //commented this one because prettier complains about it, but it works:
+    //let str3 = 'foo';
+    //expect(TypeHelpers.IsInstanceOf(str3, String)).toBe(true);
+
+    let nonStr = 3;
+    expect(TypeHelpers.IsInstanceOf(nonStr, String)).toBe(false);
+
+    let int1 = 2;
+    expect(TypeHelpers.IsInstanceOf(int1, Number)).toBe(true);
+    let int2 = Number(2);
+    expect(TypeHelpers.IsInstanceOf(int2, Number)).toBe(true);
+    let nonInt = "2";
+    expect(TypeHelpers.IsInstanceOf(nonInt, Number)).toBe(false);
+
+    let foo = new Foo();
+    let bar = new Bar();
+    expect(TypeHelpers.IsInstanceOf(foo, Foo)).toBe(true);
+    expect(TypeHelpers.IsInstanceOf(bar, Bar)).toBe(true);
+    expect(TypeHelpers.IsInstanceOf(foo, Bar)).toBe(false);
+    expect(TypeHelpers.IsInstanceOf(bar, Foo)).toBe(false);
+});
+
 export function runCommitLintOnMsg(inputMsg: string) {
     // FIXME: should we .lowerCase().startsWith("win") in case it starts
     // returning Win64 in the future? thing is, our CI doesn't like this