Recently, I encountered a challenge where I needed to integrate a pure ESM package into a non-module. Unfortunately, modifying the script to accommodate this requirement was not an option.
To tackle this issue, I turned to using the import() function (also known as a "dynamic import"). This method returns a Promise instead of the actual module, and in the absence of being able to use await due to the non-module context, I resorted to utilizing .then().
The pure ESM package in question (unist-util-visit) is utilized within a function exported by my script, which is further employed in another script. To provide some clarity, the import hierarchy goes as follows:
importer.js imports imported.js imports unist-util-visit
A perplexing problem emerged wherein any exports from within the .then() block in imported.js failed to manifest in importer.js.
This predicament persisted even after taking timing into account. In fact, I resorted to leveraging an EventEmitter to ensure that importer.js waited until the execution of imported.js's .then() block was completed:
imported.js:
const EventEmitter = require('events');
module.exports.emitter = new EventEmitter();
module.exports.outsideFxn = function () {
console.log('hello');
}
import('unist-util-visit').then((unistUtilVisit) => {
module.exports.fxn = function() {
console.log(`unistUtilVisit: ${typeof unistUtilVisit}`);
}
module.exports.emitter.emit('ready');
});
importer.js:
import('./imported.js').then((imported) => {
console.log("In importer.js's .then():");
console.log(' fxn:', imported.fxn);
console.log(' outsideFxn:', imported.outsideFxn);
imported.emitter.on('ready', () => {
console.log("After imported.js is done:")
console.log(' fxn:', imported.fxn);
});
});
Upon execution, the output observed was:
$ node importer.js
In importer.js's .then():
fxn: undefined
outsideFxn: [Function (anonymous)]
After imported.js is done:
fxn: undefined
How could this be resolved? What crucial aspect am I overlooking that prevents the proper definition of exports within the .then() function? Is there a way for me to successfully export my function?