Can I dynamically import TypeScript modules in Node.js/Express?

Question

I have a Node.js server built with Express.js and coded in TypeScript. Here's a snippet of the get call for my server:

server.ts

private get(req: Request, res: Response, next: NextFunction, objectName: string) {
    var DatabaseObject = require("./models/" + objectName + ".js")(this.orm, Sequelize.DataTypes);
    var Transform = require("./routes/" + objectName + ".js");
    var transform = new Transform();

    // ...

    console.log(req.query["columns"]);
    console.log(transform.columnWhitelist);
    console.log(transform);

    // ...

    if (transform.columnWhitelist) {
        console.log("Column Whitelist Exists.");
    }
    // ...
}

It dynamically loads the Sequelize module for the database object being requested in the URL and then tries to load a TypeScript module with rules on what columns can be selected, which columns can be queried on, etc. Here's the beginning of my ruleset class:

account.ts

export default class Transform {
    static columnWhitelist : Object = {"id": "id", "name": "name", "parentAccountId":"parentAccountId", "masterAccountId":"masterAccountId"};

    constructor() { }
}

However, running my application, I get:

id,name,parentAccountId
undefined
{ default: 
   { [Function: Transform]
     columnWhitelist: 
      { id: 'id',
        name: 'name',
        parentAccountId: 'parentAccountId',
        masterAccountId: 'masterAccountId' } } }

Making the call transform.columnWhitelist, I get undefined, despite seeing it in the generated JavaScript file as well. I've also tried just:

    var transform = require("./routes/" + objectName + ".js");

Or:

    var transform = require("./routes/" + objectName + ".js")();

But neither of these work either.

daletune · Accepted Answer · 2017-03-29 08:49:13Z

4

If you have commonjs as a module in your tsconfig.json and Transform class exported as default you should probably import it as

 var transform = require("./routes/" + objectName + ".js").default;

answered Mar 29, 2017 at 8:49

daletune

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1 Comment

NobleUplift Over a year ago

I get it now. Thanks a lot! At one point I did try var Transform = require("./routes/" + objectName + ".js"); var transform = Transform.Transform; or something like that but I must've typed something wrong.

nkweb · Accepted Answer · 2018-01-08 22:45:05Z

0

If you do not want to use

var transform = require("./routes/" + objectName + ".js").default;

You can export your class by doing

class Transform {
     static columnWhitelist: Object = {"id": "id", "name": "name", "parentAccountId": "parentAccountId", "masterAccountId": "masterAccountId"};

     constructor () {}
}

export = Transform;

After you can do again as before:

var transform = require ("./ routes /" + objectName + ".js");

answered Jan 8, 2018 at 22:45

nkweb

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2 Comments

NobleUplift Over a year ago

Is export = Transform; TypeScript-specific syntax versus the module.exports = ... of JavaScript, or another way of writing the latter?

nkweb Over a year ago

export = is used to give typescript the export default behavior. In addition it works with interfaces, functions, enums etc ... You can find out more by reading the documentation https://www.typescriptlang.org/docs/handbook/modules.html (you can do a search with export =) if you want to keep typing, you can add: var transform: typeof Transform = require("./routes/" +objectName+ ".js");

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