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

Question

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 };

Answer 1

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.

Answer 2

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

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

Answer 3

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.

Answer 4

I resolved my case by replacing import with require:

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

Answer 5

There are several common ways to resolve the conflict associated with the above issue

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

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

This is the most recommended way to fix the issue
By adding the type="module" attribute, you are telling the browser that the script should be treated as an ECMAScript module, and it should use the appropriate rules for resolving dependencies and executing the code.

---

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

{
  "type": "module",
}

Restart the project npm start

---

3. The third: replace import by require()

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');

Answer 6

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.

Answer 7

Applicable for node 12. This answer is no longer maintained for new node versions. Feel free to comment solutions for more recent versions.

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.

Answer 8

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

Answer 9

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.'));

Answer 10

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)
   ],

Answer 11

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.

Answer 12

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

And restart your application:

npm start

Then your problem is solved.

Answer 13

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.

Answer 14

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>`

Answer 15

For me this helped:

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

Answer 16

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",

Answer 17

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

Instead of   import express from 'express';

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

Answer 18

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

Answer 19

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.

Answer 20

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>

Answer 21

In my case, I updated

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

with

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

in my tsconfig.json file.

Answer 22

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

File data.js

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

By adding type=module I got CORS error.

I found out that I can import file data.js into my script.js file just by including file 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 file data.js, I just changed my HTML file to:

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

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

Answer 23

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.

Answer 24

try add .babelrc

{
"presets": [
  [
    "@babel/env",
    {
      "targets": {
        "node": "12"
      },
      "modules": "commonjs"
    }
  ]
] }

Answer 25

If you're using NextJS, maybe your code should be use on the client (brower) side only. Try replace the component in the Page by a dynamic import with "ssr: false" like this in '/pages/my-page':

[...]
const MyClientSideOnlyComponent = dynamic(() => import('../components/Component'), {ssr: false});
    
return   <MyClientSideOnlyComponent/>
[...]

instead of

return <Component/>

Answer 26

I thought I would add this note because it was not apparently obvious to me. You need to add type="module" to all script includes, not just the one you want to use for your utility file.

index.html:

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

main.js:

import myFunction from './utils.js

utils.js:

export default myFunction

Answer 27

if you want to import functions from module. let's say, main.js has func1 and func2 defined, and you want to import those to function to a new module say, test.js

Below will solve the problem.

main.js:

const func1 = () => {console.log('do sth in func1')};
const func2 = () => {console.log('do sth in func2')};

//at the end of module
//export specific functions here
module.exports = { func1, func2 };

test.js :

// import them here
const{ func1, func2} = require('./main.js');
func1();
func2();

Answer 28

Following worked, inline export gave issue but export at the end of fn following worked. const xxx = async(....)

module.exports = { xxx, };

Answer 29

If you are facing the same issue in the Cucumber TypeScript framework then the below fix is working.

In the cucumber.json file, mention as below. Install the ts-node.

{
    "default":{
        "requireModule":[
            "ts-node/register"
        ]
    }
}

Answer 30

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.