What is the meaning of empty export {} in vanilla javascript/HTML

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In the Google Maps Javascript API example, I see they had something like this in the HTML:

<script type="module" src="./index.ts"></script>

and an empty export statement at the end of the TS/JS scripts.

let map;
function initMap() {
    map = new google.maps.Map(document.getElementById("map"), {
        center: { lat: -34.397, lng: 150.644 },
        zoom: 8,
    });
}
window.initMap = initMap;
export {};

I don't see any examples or mentioning of empty exports on MDN, so I was wondering if anyone knew how it works. How does the script know to run it if the export is empty.

typescript html javascript
1 Answers

This looks like something in TypeScript; it has nothing to do with JavaScript.

If either of the cases below occurs, then you will need an import/export in the file.

  1. The TypeScript file is being called with the flag below.

    --isolatedModules

  2. The tsconfig.json file has the following key and value.

    {
  "isolatedModules": true
}

According to typescriptlang.org, it states:

If isolatedModules is set, all implementation files must be modules (which means it has some form of import/export). An error occurs if any file isn’t a module.

If you try to run the TypeScript file with the --isolatedModules flag, you get an error like below.

'index.ts' cannot be compiled under '--isolatedModules' because it is considered a global script file. Add an import, export, or an empty 'export {}' statement to make it a module.

As the error states above, the simplest way to fix the issue without adding any unnecessary import statements and/or export statements, it is easiest to export an empty object ({}), like so.

export {};

In summary, the empty object export will not do anything in JavaScript (or TypeScript, without the --isolatedModules flag). However, it comes in handy when running with the --isolatedModules flag.

The Google Maps JavaScript API example might be getting ready for this scenario, in case someone copied-and-pasted the code, so that they wouldn't get an error.

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