Why do I get errors like these when I try to use the new Node.js support for ES6 modules (e.g. with node --experimental-modules script.mjs)?
// script.mjs
import * as fs from 'fs';
// TypeError: fs.readFile is not a function
fs.readFile('data.csv', 'utf8', (err, data) => {
if (!err) {
console.log(data);
}
});
// TypeError: fs.readdirSync is not a function
fs.readdirSync('.').forEach(fileName => {
console.log(fileName);
});
You must use import fs from 'fs', not import * as fs from 'fs'.
This is because (at least from the point of view of mjs files) the 'fs' module exports only one thing, which is called default. So if you write import * as fs from 'fs', fs.default.readFile exists but fs.readFile does not. Perhaps the same is true of all Node.js (CommonJS) modules.
Confusingly, in TypeScript modules (with @types/node and ES5 output), import fs from 'fs' produces error
error TS1192: Module '"fs"' has no default export
so in TypeScript you must write import * as fs from 'fs'; by default. It appears this can be changed to match the way mjs files work using the new "esModuleInterop": true option in tsconfig.json.
fs is a core module in node, you don't need to import it at all. It's always there.
ReferenceError: fs is not defined, even if it's not an .mjs module.
var fs = require('fs'); but we have to do some trickery for TS to get it just right. I was able to get it using Import * as fs from 'fs';, but not Import fs from 'fs';. I have been able to do the latter with most node modules when enabling the esModuleInterop and allowSyntheticDefaultImports, but not fs :( This one does work, for example: import path from 'path';We can simply import like this it in our code
import * as fs from 'fs';
and it is perfectly working for me, give it a try
Adding "esModuleInterop": true in my tsconfig.json file fixed the issue
For recent ES versions (as ES2020 for example), the good way to do this is :
import { readFileSync, writeFileSync } from 'fs';
then in your code, simply use it
const cfg = readFileSync("./toto.json", "utf8");
