“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="redirect/?url=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 };

10 Answers

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>

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 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

I resolved my case by replacing “import” by “require”.

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

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 before I referred 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)
   ],

Update For Node / NPM

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

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

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.

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>

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