JavaScript - How to make ES6 imports work in browser?

问题

I'm starting a new project in which I'd like to have ES6 style modules, however, I can't get it to run in a browser. I'm using Chrome.

I isolated the issue into very few lines of code.

Here are my 2 TypeScript files:

app.ts

import { Component } from './component';

var component: Component = new Component();

component.ts

export class Component {

}

Here's how they compile to JavaScript:

app.js

import { Component } from './component';
var component = new Component();

component.js

export class Component {
}

My index.html only contains a script tag. I tried a few variations, but none of them worked.

index.html #1

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

The script is not loaded. (No request in network tab)

index.html #2

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

The script is not loaded. (No request in network tab)

index.html #3

<script src="src/app.js"></script>

Uncaught SyntaxError: Unexpected token {

I'm using tsc to transpile TypeScript via Visual Studio Code.

tasks.json

{
    "version": "2.0.0",
    "tasks": [
        {
            "type": "typescript",
            "tsconfig": "tsconfig.json",
            "problemMatcher": [
                "$tsc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "presentation": {
                "reveal": "silent"
            }
        }
    ]
}

tsconfig.json

{
  "compilerOptions": {
    "target": "es6",
    "sourceMap": false,
    "removeComments": false,
    "noImplicitReturns": true,
    "noImplicitAny": true,
    "preserveConstEnums": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "outDir": "../src/"
  },
  "exclude": [
    "logs",
    "node_modules"
  ]
}

回答1:

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 tadk runner like grunt 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!";
}

来源：https://stackoverflow.com/questions/53023279/javascript-how-to-make-es6-imports-work-in-browser

标签

javascript

ecmascript-6

es6-modules

es6-module-loader