Blazor project - require not defined

I'm trying to get Typescript modules working in a Blazor project. This is a brand new project, freshly created, with no twiddling of project settings by yours truly.

I get the error:

Uncaught ReferenceError ReferenceError: require is not definedat (d:\Code\ScratchPad\TestApp2\wwwroot\TS\ModTest.ts:2:1)

I get it that browsers don't support require. But why is a brand new client-side Blazor app outputting code that browsers won't work with? Obviously I must be missing something but what?

TestTs.razor:

@page "/TSTest"@inject IJSRuntime JSRuntime<script src="/TS/ModTestSub.js" type="text/javascript"></script><script src="/TS/ModTest.js" type="text/javascript"></script><h1>Typescript test</h1><button @onclick=LoadTS>Load TS file</button>@code{   async void LoadTS()   {      var objModTest = await JSRuntime.InvokeAsync<IJSObjectReference>("GetModTest");      await objModTest.InvokeVoidAsync("ShowMsg");   }}

ModTest.ts:

import * as SubMod from "./ModTestSub"class ModTest {   public ShowMsg() {      SubMod.SubShowMsg();   }}export function GetModTest(): ModTest {   var result = new ModTest();   return result;}

ModTest.js (emitted code):

"use strict";Object.defineProperty(exports, "__esModule", { value: true });exports.GetModTest = GetModTest;var SubMod = require("./ModTestSub");var ModTest = /** @class */ (function () {    function ModTest() {    }    ModTest.prototype.ShowMsg = function () {        SubMod.SubShowMsg();    };    return ModTest;}());function GetModTest() {    var result = new ModTest();    return result;}//# sourceMappingURL=ModTest.js.map

ModTestSub.ts

export function SubShowMsg() {   alert("Sub show message");}

ModTestSub.js (emitted code):

"use strict";Object.defineProperty(exports, "__esModule", { value: true });exports.SubShowMsg = SubShowMsg;function SubShowMsg() {    alert("Sub show message");}//# sourceMappingURL=ModTestSub.js.map