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How to create an express Application with import instead of require

2

This is what works with require. We instead want it to use import.

import Request, Response, Application from 'express';

// TODO Figure out how NOT to use require here.
const express = require('express');
var app: Application = express();

app.get('/', function (req: Request, res: Response) 
 res.send('Hello World')
);

app.listen(3000);

What we have tried

Our tsconfig.json has "esModuleInterop": true.

Attempt # 1

import express from 'express';

That gives this error:

"node_modules/@types/express/index"' has no default export.ts

Attempt # 2

import * as express from 'express';
var app = express();

That gives a different error:

Cannot invoke an expression whose type lacks a call signature. Type 'typeof e' has no compatible call signatures.ts(2349)
index.ts(1, 1): Type originates at this import. A namespace-style import cannot be called or constructed, and will cause a failure at runtime. Consider using a default import or import require here instead.

typescript express

share|improve this question

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I can tell you why Attempt #2 didn't work: You asked for a module namespace object, then tried to run it as a function.
  
  – T.J. Crowder
  Mar 6 at 18:30
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Looks like @types/express is missing the fact that Express provides a default export that's a function. (I just double-checked that it does, and that import express from "express"; correctly retrieves it in JavaScript code with --experimental-modules enabled.) So definitely a types thing (as the error suggests). Looking in node_modules/@types/express/index.d.ts, I see that it at least tries to define an export for the express function: "Creates an Express application. The express() function is a top-level function exported by the express module."
  
  – T.J. Crowder
  Mar 6 at 18:35
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @T.J.Crowder Doing a forced cast to a Function works: const app = (express as unknown as Function)();. It's certainly an ugly hack, though.
  
  – Shaun Luttin
  Mar 6 at 19:02
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  (Speaking of hacks: import * as mno from 'express'; const express = mno.default as unknown as Function;) But the real solution (which sadly I can't help with) is to sort out the types in @types/express/index.d.ts and/or TypeScript's use of them.
  
  – T.J. Crowder
  Mar 6 at 19:14
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Sorting out the types would be a worthwhile pull request. I can add that to my "maybe someday" list of things to do.
  
  – Shaun Luttin
  Mar 6 at 21:00
  

  
  
  
  

 | 
show 6 more comments

2

This is what works with require. We instead want it to use import.

import Request, Response, Application from 'express';

// TODO Figure out how NOT to use require here.
const express = require('express');
var app: Application = express();

app.get('/', function (req: Request, res: Response) 
 res.send('Hello World')
);

app.listen(3000);

What we have tried

Our tsconfig.json has "esModuleInterop": true.

Attempt # 1

import express from 'express';

That gives this error:

"node_modules/@types/express/index"' has no default export.ts

Attempt # 2

import * as express from 'express';
var app = express();

That gives a different error:

Cannot invoke an expression whose type lacks a call signature. Type 'typeof e' has no compatible call signatures.ts(2349)
index.ts(1, 1): Type originates at this import. A namespace-style import cannot be called or constructed, and will cause a failure at runtime. Consider using a default import or import require here instead.

typescript express

share|improve this question

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I can tell you why Attempt #2 didn't work: You asked for a module namespace object, then tried to run it as a function.
  
  – T.J. Crowder
  Mar 6 at 18:30
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Looks like @types/express is missing the fact that Express provides a default export that's a function. (I just double-checked that it does, and that import express from "express"; correctly retrieves it in JavaScript code with --experimental-modules enabled.) So definitely a types thing (as the error suggests). Looking in node_modules/@types/express/index.d.ts, I see that it at least tries to define an export for the express function: "Creates an Express application. The express() function is a top-level function exported by the express module."
  
  – T.J. Crowder
  Mar 6 at 18:35
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @T.J.Crowder Doing a forced cast to a Function works: const app = (express as unknown as Function)();. It's certainly an ugly hack, though.
  
  – Shaun Luttin
  Mar 6 at 19:02
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  (Speaking of hacks: import * as mno from 'express'; const express = mno.default as unknown as Function;) But the real solution (which sadly I can't help with) is to sort out the types in @types/express/index.d.ts and/or TypeScript's use of them.
  
  – T.J. Crowder
  Mar 6 at 19:14
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Sorting out the types would be a worthwhile pull request. I can add that to my "maybe someday" list of things to do.
  
  – Shaun Luttin
  Mar 6 at 21:00
  

  
  
  
  

 | 
show 6 more comments

This is what works with require. We instead want it to use import.

import Request, Response, Application from 'express';

// TODO Figure out how NOT to use require here.
const express = require('express');
var app: Application = express();

app.get('/', function (req: Request, res: Response) 
 res.send('Hello World')
);

app.listen(3000);

What we have tried

Our tsconfig.json has "esModuleInterop": true.

Attempt # 1

import express from 'express';

That gives this error:

"node_modules/@types/express/index"' has no default export.ts

Attempt # 2

import * as express from 'express';
var app = express();

That gives a different error:

Cannot invoke an expression whose type lacks a call signature. Type 'typeof e' has no compatible call signatures.ts(2349)
index.ts(1, 1): Type originates at this import. A namespace-style import cannot be called or constructed, and will cause a failure at runtime. Consider using a default import or import require here instead.

typescript express

share|improve this question

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292

import Request, Response, Application from 'express';

// TODO Figure out how NOT to use require here.
const express = require('express');
var app: Application = express();

app.get('/', function (req: Request, res: Response) 
 res.send('Hello World')
);

app.listen(3000);

import express from 'express';

import * as express from 'express';
var app = express();

share|improve this question

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292

share|improve this question

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292

asked Mar 6 at 18:21

Shaun LuttinShaun Luttin

61.5k34233292