Which Browsers Support Import and Export Syntax for Ecmascript 6

Which browsers support import and export syntax for ECMAScript 6?

Chrome and Firefox support import and export syntax (there exists tests for proper parsing).

What isn't supported is module loading - you can't load module by any means, because specification for it isn't complete. You have to use some kind of module bundler for this. I'm not front-end developer, but I have heard good opinions on Rollup from my coworkers.

How will browsers handle ES6 import/export syntax

This is standardized now and supported by all major modern browsers.

will the modules be loaded asynchronously?

Yes, with two options available; details below.

Referencing only my main or entry file and browsers will lazy load the requiere modules.

Not so much "lazy," but yes.

Enabling it

Details in the spec here and here (and possibly elsewhere).

To get this behavior, you specify that your script is a module by using type="module":

<script src="main.js" type="module"></script>

or for inline scripts

<script type="module">
// ...module code here
</script>

That means that the script is parsed and handled per the Module definition in the JavaScript specification instead of per the Script definition, which means it can have imports (and exports).

Imports are resolved relative to the script's URL (for modules loaded via a separate resource such as the main.js above, just like CSS) or relative to the document (for inline modules like the one above).

So for instance, if I have this in my document at http://example.com/index.html:

<script src="./handy/stuff/nifty.js" type="module"></script>

...and nifty.js contains

import Thingy from "./thingy.js";

...then the browser looks for http://example.com/handy/stuff/thingy.js, not http://example.com/thingy.js. Again, just like CSS imports.

Note that the ./ on that module specifier is required, just from "thingy.js" won't work. That's because bare specifiers are disallowed because they'll probably end up having a special meaning. (For instance, in Node.js, that's how you specify built-in modules, and modules installed in node_modules.) A module specifier must be a full URL, or a relative URL starting with /, ./, or ../.

Async

I said above that modules are loaded asynchronously, and there are two options available. This graphic from the spec says it best (see the spec for the latest copy of it):

As you can see, for type="module" scripts, if you don't put any special flag attributes on the script tag, all of the module's dependencies will be resolved and then the script will be run once parsing of the HTML is complete. If you include the async attribute, it may run sooner, before the HTML parsing is complete (for instance, if all the scripts are in cache). (defer is not valid for modules.)

JavaScript - How to make ES6 imports work in browser?

To be honest - I think this is a good question because JS is widely use in both server-side and client-side application, which contributes to the already existing confusion among developers

It's clear that your TS code is written as server-side code (probably on Node.js). Trying to run it (as is) on client-side is... well.. tricky. The reason: The syntax you are using in your code suppose to run on server-side (not on client-side). Is there a workaround? Well... yes!

The good news:

JS ES6 does have a native module loader! (check MDN)

The bad ones:

• Syntax is different from Node.js module loader syntax (when exporting a module)
• Support is very partial (modern browsers only)

Some additional notes:

• The common syntax of modules loading is associated with a third-party library called require js (https://requirejs.org/). You can use this library in client side projects but you have to install it and configure it properly (the docs are pretty clear about how to do that)
• You can always use a task runner like grunt (https://gruntjs.com/) or similar projects to assist you to minify and unify all your code to a single file in production. Why you ask? It will clearly help you ease the load when a client fetch you website (less files are better in terms of network traffic)

As you see, there is no quick or simple answer to your question.. but it may be a good starting point to improve your knowledge and building better modern web apps.

UPDATE

As requested, I created a little sandbox demo that shows how to use ES6 native module (https://codesandbox.io/s/oj2rwm9v35)

index.html

<html>
<body>
    <div id="app"></div>
    <script type="module" src="src/primary.js"></script>
</body>
</html>

primary.js

import test from "./test";

test();

test.js

export default function test() {
  document.querySelector("#app").textContent = "Hello JS module!";
}

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