Let's say I have a variable that I want to export. What's the difference between
export const a = 1;
vs
export let a = 1;
I understand the difference between const and let, but when you export them, what are the differences?
In ES6, imports are live read-only views on exported-values. As a result, when you do import a from "somemodule";, you cannot assign to a no matter how you declare a in the module.
However, since imported variables are live views, they do change according to the "raw" exported variable in exports. Consider the following code (borrowed from the reference article below):
//------ lib.js ------
export let counter = 3;
export function incCounter() {
counter++;
}
//------ main1.js ------
import { counter, incCounter } from './lib';
// The imported value `counter` is live
console.log(counter); // 3
incCounter();
console.log(counter); // 4
// The imported value can’t be changed
counter++; // TypeError
As you can see, the difference really lies in lib.js, not main1.js.
To summarize:
import-ed variables, no matter how you declare the corresponding variables in the module.let-vs-const semantics applies to the declared variable in the module.
const, it cannot be reassigned or rebound in anywhere.let, it can only be reassigned in the module (but not the user). If it is changed, the import-ed variable changes accordingly.myModule.counter = "new value". As you explained it did not work. I am a bit disappointed that oxc did not find out that.I think that once you've imported it, the behaviour is the same (in the place your variable will be used outside source file).
The only difference would be if you try to reassign it before the end of this very file.
let variable will be seen whenever they occur, even after the exporting module has finished evaluation. See example in answer by @FelisCatus.
exportkeyword details here. Currently it is not supported natively by any of the web-browsers.