javascript - Correct async function export in node.js

Question

I had my custom module with following code:

module.exports.PrintNearestStore = async function PrintNearestStore(session, lat, lon) {
...
}

It worked fine if call the function outside my module, however if I called inside I got error while running:

(node:24372) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): ReferenceError: PrintNearestStore is not defined

When I changed syntax to:

module.exports.PrintNearestStore = PrintNearestStore;

var PrintNearestStore = async function(session, lat, lon) {

}

It started to work fine inside module, but fails outside the module - I got error:

(node:32422) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): TypeError: mymodule.PrintNearestStore is not a function

So I've changed code to:

module.exports.PrintNearestStore = async function(session, lat, lon) {
    await PrintNearestStore(session, lat, lon);
}

var PrintNearestStore = async function(session, lat, lon) {
...
}

And now it works in all cases: inside and outside. However want to understand semantics and if there is more beautiful and shorter way to write it? How to correctly define and use async function both: inside and outside (exports) module?

Answer 1

This doesn't really have anything to with async functions specially. If you want to call a function internally and export it, define it first and then export it.

async function doStuff() {
  // ...
}
// doStuff is defined inside the module so we can call it wherever we want

// Export it to make it available outside
module.exports.doStuff = doStuff;

---

Explanation of the problems with your attempts:

module.exports.PrintNearestStore = async function PrintNearestStore(session, lat, lon) {
...
}

This does not define a function in the module. The function definition is a function expression. The name of a function expression only creates a variable inside the function itself. Simpler example:

var foo = function bar() {
  console.log(typeof bar); // 'function' - works
};
foo();
console.log(typeof foo); // 'function' - works
console.log(typeof bar); // 'undefined' - there is no such variable `bar`