import.meta is empty

[davidmz]

I'm trying to use the gifsicle package in one of my projects, and have an import.meta.url issue. Here is a simple repo that reproduces the problem: https://github.com/davidmz/gifsicle-esbuild-test

Try to compile code with the npm run build command and then run it with npm run run. You will see the ERR_INVALID_URL error. This line of gifsicle code uses the import.meta.url:

const pkg = JSON.parse(fs.readFileSync(new URL('../package.json', import.meta.url)));

and esbuild compiled it to the:

var import_meta = {};
var pkg = JSON.parse(import_node_fs.default.readFileSync(new URL("../package.json", import_meta.url)));

What do I (or, maybe, the gifsicle authors) wrong?

[hyrious]

You have to make the code work:

fs.readFileSync(new URL('../package.json', import.meta.url))

In 2 ways,

• Don't bundle that library. You can add --external:gifsicle to your build command so that this code will not change and it will work if your node runtime supports import.meta.
• Modify this code to be bundle-able. You can write a plugin to replace this line with what it expects (the contents of the package.json).

Why is import.meta.url not bundle-able? Because this is a runtime feature, it only exists in ESM context. So esbuild will add var import_meta = {} in non-ESM formats (like CJS/IIFE) to make it not a syntax error. In which case not all users want this result. However doing polyfill about this thing is also not always correct. I'll show you why in your example:

import.meta.url is path/to/node_modules/gifsicle/lib/index.js when it is in the source code. However, when it gets bundled, it becomes path/to/out.js. See the difference?

[evanw]

Thanks for the comment. I agree that making gifsicle external makes the most sense here, as it's not easy to bundle. Gifsicle also appears to invoke a native binary executable so bundling it also doesn't make sense for that reason. Even if you were to bundle it somehow, you would still need to keep the node_modules file around anyway since I assume gifsicle wouldn't work without the binary executable.

Closing as "working as intended."

[davidmz]

Thank you so much for the detailed explanations!