Prisma seed - cannot read properties of undefined (reading 'findFirst') - node.js

Question

I have a weird issue using prisma seed that I've never faced before and struggling to understand what causes it. The app is hosted in a nextjs full-stack project.
I have the following prisma init script:
const prisma = new PrismaClient();
export default prisma;
When using prisma in my app (next dev), everything works and the queries are being executed.
When I try to run the seed script however, it fails with TypeError: Cannot read properties of undefined (reading 'findFirst')
Here is the seed script:
async function main() {
const existingUser = await db.user.findFirst();
// ...not relevant
}
main()
.then(async () => await db.$disconnect())
.catch(async e => {
console.error(e);
await db.$disconnect();
process.exit(1);
});
package.json prisma section:
"prisma": {
"seed": "ts-node src/server/db/seed.ts",
"schema": "src/server/db/schema.prisma"
},
tsconfig.json ts-node section:
"ts-node": {
"require": ["tsconfig-paths/register"],
"transpileOnly": true,
"compilerOptions": {
"module": "commonjs"
}
},
Printing the prisma client on the seed script returns {}, instead of the actual instance that I can see while printing in dev mode.
Any ideas are welcome, thanks!

Answer 1

A few debugging hours later, I finally found the issue. This code fragment is located in the prisma runtime config:
const dmmfModelKeys = Object.keys(client._baseDmmf.modelMap);
const jsModelKeys = dmmfModelKeys.map(dmmfToJSModelName);
const allKeys = [...new Set(dmmfModelKeys.concat(jsModelKeys))];
I have seen that while the first 2 variables were outputting a result, creating a new Set was actually returning an empty array, instead of the real value.
By default, NextJS uses es5 as a target in tsconfig. ES5 however does not yet have the Set construct, which was causing the problem.
Upgrading to es2015 solved the problem.
I was just expecting some kind of an error, instead of silent fail..