"Uncaught SyntaxError: Cannot use import statement outside a module" when importing ECMAScript 6

I'm using ArcGIS JSAPI 4.12 and wish to use Spatial Illusions to draw military symbols on a map.

When I add milsymbol.js to the script, the console returns error

> Uncaught SyntaxError: Cannot use import statement outside a module`

so I add type="module" to the script, and then it returns

> Uncaught ReferenceError: ms is not defined

Here's my code:

<link rel="stylesheet" href="https://js.arcgis.com/4.12/esri/css/main.css">
<script src="https://js.arcgis.com/4.12/"></script>
<script type="module" src="milsymbol-2.0.0/src/milsymbol.js"></script>

<script>
    require([
        "esri/Map",
        "esri/views/MapView",
        "esri/layers/MapImageLayer",
        "esri/layers/FeatureLayer"
    ], function (Map, MapView, MapImageLayer, FeatureLayer) {

        var symbol = new ms.Symbol("SFG-UCI----D", { size: 30 }).asCanvas(3);
        var map = new Map({
            basemap: "topo-vector"
        });

        var view = new MapView({
            container: "viewDiv",
            map: map,
            center: [121, 23],
            zoom: 7
        });
    });
</script>

So, whether I add type="module" or not, there are always errors. However, in the official document of Spatial Illusions, there isn't any type="module" in the script. I'm now really confused. How do they manage to get it work without adding the type?

File milsymbol.js

import { ms } from "./ms.js";

import Symbol from "./ms/symbol.js";
ms.Symbol = Symbol;

export { ms };

I got this error because I forgot the type="module" inside the script tag:

<script type="module" src="milsymbol-2.0.0/src/milsymbol.js"></script>

Update For Node.js / NPM

Add "type": "module" to your package.json file.

{
  // ...
  "type": "module",
  // ...
}

Note: When using modules, if you get ReferenceError: require is not defined, you'll need to use the import syntax instead of require. You can't natively mix and match between them, so you'll need to pick one or use a bundler if you need to use both.

It looks like the cause of the errors are:

1. You're currently loading the source file in the src directory instead of the built file in the dist directory (you can see what the intended distributed file is here). This means that you're using the native source code in an unaltered/unbundled state, leading to the following error: Uncaught SyntaxError: Cannot use import statement outside a module. This should be fixed by using the bundled version since the package is using rollup to create a bundle.

2. The reason you're getting the Uncaught ReferenceError: ms is not defined error is because modules are scoped, and since you're loading the library using native modules, ms is not in the global scope and is therefore not accessible in the following script tag.

It looks like you should be able to load the dist version of this file to have ms defined on the window. Check out this example from the library author to see an example of how this can be done.

I resolved my case by replacing "import" by "require".

// import { parse } from 'node-html-parser';
const parse = require('node-html-parser');

I was also facing the same issue until I added the type="module" to the script.

Before it was like this

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

And after changing it to

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

It worked perfectly.

I solved this issue by doing the following:

When using ECMAScript 6 modules from the browser, use the .js extension in your files, and in the script tag add type = "module".

When using ECMAScript 6 modules from a Node.js environment, use the extension .mjs in your files and use this command to run the file:

node --experimental-modules filename.mjs

Edit: This was written when node12 was the latest LTS, this does not apply to node 14 LTS.

I don't know whether this has appeared obvious here. I would like to point out that as far as client-side (browser) JavaScript is concerned, you can add type="module" to both external as well as internal js scripts.

Say, you have a file 'module.js':

var a = 10;
export {a};

You can use it in an external script, in which you do the import, eg.:

<!DOCTYPE html><html><body>
<script type="module" src="test.js"></script><!-- Here use type="module" rather than type="text/javascript" -->
</body></html>

test.js:

import {a} from "./module.js";
alert(a);

You can also use it in an internal script, eg.:

<!DOCTYPE html><html><body>
<script type="module">
    import {a} from "./module.js";
    alert(a);
</script>
</body></html>

It is worthwhile mentioning that for relative paths, you must not omit the "./" characters, ie.:

import {a} from "module.js";     // this won't work

For me, it was caused by not referencing a library (specifically typeORM, using the ormconfig.js file, under the entities key) to the src folder, instead of the dist folder...

   "entities": [
      "src/db/entity/**/*.ts", // Pay attention to "src" and "ts" (this is wrong)
   ],

instead of

   "entities": [
      "dist/db/entity/**/*.js", // Pay attention to "dist" and "js" (this is the correct way)
   ],

There are three ways to solve this:

1. The first: In the script, include type=module

    <script type="module" src="milsymbol-2.0.0/src/milsymbol.js"></script>

2. The second: In node.js, into your package.json file

    {
        // ...
        "type": "module",
        // ...
    }

3. The third: replace import by required

> Try this

import { parse } from 'node-html-parser';
parse = require('node-html-parser');

> Else try this

//import { parse } from 'node-html-parser';
parse = require('node-html-parser');

I got this error in React and fixed it with the following steps:

1. Go to the project root directory, and open the Package.json file for editing.

2. Add "type":"module";

3. Save it and restart the server.

If you want to use import instead of require() for modules, change or add the value of type to module in package.json file

Example:

package.json file

{
  "name": "appsample",
  "version": "1.0.0",
  "type": "module",
  "description": "Learning Node",
  "main": "app.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Chikeluba Anusionwu",
  "license": "ISC"
}

import http from 'http';

var host = '127.0.0.1',
    port = 1992,
    server = http.createServer();

server.on('request', (req, res) => {
  res.writeHead(200, {"Content-Type": "text/plain"});
  res.end("I am using type module in package.json file in this application.");
});

server.listen(port, () => console.log(
    'Listening to server ${port}. Connection has been established.'));

I'm coding on vanilla JavaScript. If you're doing same, simply add a type="module" to your script tag.

That is, previous code:

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

Updated code:

<script type="module" src="./index.js"></script>`

Add "type": "module", to your package.json file.

And restart your application:

npm start

Then your problem is solved.

For me this helped:

1. In the .ts file I used: import prompts from "prompts";
2. And used "module": "commonjs" in file tsconfig.json

Why this occurs and more possible causes:

A lot of interfaces still do not understand ES6 JavaScript syntax/features. Hence there is need for ES6 to be compiled to ES5 whenever it is used in any file or project.

The possible reasons for the SyntaxError: Cannot use import statement outside a module error is you are trying to run the file independently. You are yet to install and set up an ES6 compiler such as Babel or the path of the file in your runscript is wrong/not the compiled file.

If you will want to continue without a compiler, the best possible solution is to use ES5 syntax, which in your case would be var ms = require(./ms.js);. This can later be updated as appropriate or better still set up your compiler and ensure your file/project is compiled before running and also ensure your run script is running the compiled file usually named dist, build or whatever you named it and the path to the compiled file in your runscript is correct.

The error is triggered because the file you're linking to in your HTML file is the unbundled version of the file. To get the full bundled version you'll have to install it with npm:

npm install --save milsymbol

This downloads the full package to your node_modules folder.

You can then access the standalone minified JavaScript file at node_modules/milsymbol/dist/milsymbol.js

You can do this in any directory, and then just copy the below file to your /src directory.

Use this code. It worked well for me:

Add this script tag to file index.html:

<script type="module">
    import { ms } from "./ms.js";
    import Symbol from "./ms/symbol.js";
</script>

In my case, I updated

"lib": [
      "es2020",
      "dom"
    ]

with

"lib": [
  "es2016",
  "dom"
]

in my tsconfig.json file.

I ran into this error while trying to use import Express.js.

Instead of   import express from 'express';

I used   const express = require('express');

I have faced the same error by EXPO.

Mainly the solution is that to add "type": "module", in the package.json file.

However, you have to check that which is your correct package.json.

In my case, there are two package.json files, then you should add that to the server file.

To identify which is correct package.json, find "scripts": { "test": "echo \"Error: no test specified\" && exit 1" },

Below ↑　this line, add "type": "module",

I just added "type": "module" to my Package.json file and it worked for me.

I had to import some data from an external file (js file), to my script.js present in my html file.

data.js

const data = {a: 1, b: 2}

By adding type=module I got cors error.

I found out that I can import data.js into my script.js just by including data.js inside my html file.

For example, Previously my html file consists of

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

As I required some data from data.js, I just changed my html file to

<script src="assets/data.js"></script>
<script src="assets/script.js"></script>

i.e include data.js before script.js, giving access to my data variable inside script.js

It's because you haven't exported. The .ts file requires an export class format, whereas in a .js file we would use the exports function.

So, we have to use var_name = require("<pathfile>") to use those file functions.

Well, in my case, I didn't want to update my package.json file and change the file type to mjs.

So I was looking around and found out that changing the module in file tsconfig.json affected the result. My ts.config file was:

{
  "compilerOptions": {
    "target": "es2020",
    "module": "es2020",
    "lib": [
      "es2020",
    ],
    "skipLibCheck": true,
    "sourceMap": true,
    "outDir": "./dist",
    "moduleResolution": "node",
    "removeComments": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "noImplicitThis": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "resolveJsonModule": true,
    "baseUrl": "."
  },
  "exclude": [
    "node_modules"
  ],
  "include": [
    "./src/**/*.ts"
  ]
}

Like this and changing the module from "module": "es2020" to "module" : "commonjs" solved my issue.

I was using MikroORM and thought maybe it doesn't support any module above CommonJS.

None of the provided answers worked for me, but I found a different solution from: How to enable ECMAScript 6 imports in Node.js

Install ESM:

npm install --save esm

Run with ESM:

node -r esm server.js

In node JS when we use import statement instead of require it gives this type of error ex. Use const express = require('express');

Instead of import express from 'express';

Just add .pack between the name and the extension in the <script> tag in src.

I.e.:

<script src="name.pack.js">
    // Code here
</script>

This error occurs when it fails in Babel transpile.