TypeScript ES dynamic `import()`

node.js typescript ts-node typescript2.4

10,406

This is a bug in the Typescript Compiler which will be fixed in 2.5.

Exporting a default object with a function that imports a file will not compile the import statement into a require statement in Typescript 2.4.x.

For example, while this:

export const sudo = { run() { return import('./test3'); } }

Will compile to this:

exports.sudo = { run: function () { return Promise.resolve().then(function () { return require('./test3'); }); } };

This:

export default { run() { return import('./test3'); } }

Compiles into this:

exports.default = { run: function () { return import('./test3'); } };

Which is obviously wrong. A temporary solution would be this:

export const sudo = { run() { return import('./test3'); } }

export default sudo;

Which compiles (correctly) into this:

exports.sudo = { run: function () { return Promise.resolve().then(function () { return require('./test3'); }); } };
exports.default = exports.sudo;

10,406

Roomy

Updated on June 04, 2022

Comments

Roomy almost 2 years
While using the new TypeScript feature, so called ES Dynamic Imports, I am not able to run the code of my isomorphic app on the server side using ts-node.

It seems like the error does not occur when using the webpack module loader which transpiles the code in it's own way and running resulting files in a browser.

The error which I've got:
```
case 0: return [4 /*yield*/, import("./component/main")];
                             ^^^^^^
SyntaxError: Unexpected token import
```
Usually TypeScript transpiles the import expression to something like that: Promise.resolve(require("./component/main")), but I can't see it there.

How to fix that? Does it have something common with ts-node? Or there is a "polyfill" for node.js?

My tsconfig.json file:
```
{
  "compilerOptions": {
    "declaration": false,
    "emitDecoratorMetadata": true,
    "allowJs": false,
    "experimentalDecorators": true,
    "importHelpers": true,
    "inlineSourceMap": false,
    "inlineSources": false,
    "lib": [
      "DOM",
      "ES5",
      "ES6",
      "ES7"
    ],
    "listFiles": false,
    "module": "commonjs",
    "noEmitOnError": true,
    "noImplicitAny": true,
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "preserveConstEnums": false,
    "pretty": false,
    "removeComments": false,
    "strict": true,
    "target": "es5"
  }
}
```
the code:
```
import * as m from "mithril";

import LayoutComponent from "./component/layout";

const render = (
    layout: m.ComponentTypes<any, any>,
) => ({ tag, attrs }: m.Vnode<any, any>) => m(layout, attrs, m(tag as any, attrs));

export default {
    "/:path...": {
        onmatch: async (args, path) => (await import("./component/main")).default,
        render: render(LayoutComponent),
    },
} as m.RouteDefs;
```
- Roomy almost 7 years
  
  it didn't worked, sorry
- Roomy almost 7 years
  
  > tsc "--version" Version 2.4.2, > ts-node "--version" ts-node v3.3.0 node v8.2.1 typescript v2.4.2
- Aluan Haddad almost 7 years
  
  "lib": ["dom", "esnext"] would be better. Not saying it's the issue but I advise changing it.
- Michael Fedora
  
  I replicated the error, working on solution now...
- Michael Fedora
  
  Are you using local (node_modules) tsc/ts-node or global? Are those local/global versions? If you're running linux, does sudo have different version than your local user? etc. That's the only other things I can think of.
- Aluan Haddad
  
  To get this to work I had to pass the --compiler argument explicitly to ts-node. Make it is using the correct version of typescript.
- Roomy
  
  @edit I've pasted the code which is used
- Roomy
  
  @edit - updated by tsconfig.json
- Michael Fedora
  
  tsc --version gives you what?
Roomy almost 7 years

Okay, so in other words I'm forced to use Promise instead of async/await? import(...).then((cmp) => cmp.default) should do the trick, am I correct?
Michael Fedora almost 7 years

No; you are forced to export a non-default object, and then export default that object. Async/await will still work (afaik, I can keep trying)
Roomy almost 7 years

yep, you are right, I can not use that syntax, thanks for explaining that
Michael Fedora almost 7 years

You can still keep the rest of your code the same (using the "default" object, etc), just make sure you are also exporting a sudo-default first, and then exporting said sudo-default as the "default" so that it compiles correctly.
Frank Nocke over 6 years

I am on Typescript 2.5.3 (judged from package.version and yarn list) and the bug is still present.
Michael Fedora over 6 years

Seems to be fixed in 2.6.
chharvey about 5 years

off-topic question, but what’s the difference between Promise.resolve().then(() => require('./test3')) and Promise.resolve(require('./test3'))?
Michael Fedora about 5 years

the first will run the lambda function when the promise is resolved, the second will run the require function before it is resolved, because you are not passing a function there but rather the result of the require() call.