transferring libraries via functions in TypeScript

Question

transferring libraries via functions in TypeScript

As I work on developing my app, I have decided to implement the dependency-injection pattern. In passing mongoose and config libraries as parameters, I encountered an issue with the config library. Specifically, when hovering over config.get('dbUri'), an error message pops up saying: 'Untyped function calls may not accept type arguments.ts(2347)'

app.ts

(async () => await initializeDatabaseConnection(mongoose, config))();

connect.ts

async function initializeDatabaseConnection(mongoose: any, config: any):Promise<void>{
    try {
        const dbUri = config.get<string>('dbUri');
        
        await mongoose.connect(dbUri, () => {
            console.log('connected to the database successfully!');
        });
    } catch (error) {
        process.exit(1)
    }
}

export default initializeDatabaseConnection;

typescript function dependency-injection parameters libraries

Answer 1

Answer №1

You have entered the value config as any, and then attempted to use it as if it were a generic parameter. However, since any signifies that TypeScript does not know the type of this variable, you cannot treat it as having a generic parameter.

To quickly resolve this issue, eliminate the <string>:

const dbUri = config.get('dbUri');

Nevertheless, a strongly-typed solution would be more appropriate in this scenario.

The type for mongoose is likely the type imported from import mongoose from 'mongoose'. It appears you will need to obtain the typeof mongoose since the package may not export a specific type for this purpose.

Subsequently, you must type config based on its actual type. Assuming your config resembles something like:

class ConfigService {
  get<T>(prop: string): T {
    return someConfigObject[prop]
  }
}

And at some point during dependency injection, you instantiate an object of that class.

Following these steps, you can specify the type for connectDb as shown below:

import type mongooseGlobal from 'mongoose'

async function connectDb(
  mongoose: typeof mongooseGlobal,
  config: ConfigService
): Promise<void>{
  //...
}

The key takeaway here is that you must determine the type of the object you wish to pass as a parameter to a function. If an appropriate type already exists, utilize it. If not, utilize typeof to derive the type from a given value.

Playground

Answer 2

You have entered the value config as any, and then attempted to use it as if it were a generic parameter. However, since any signifies that TypeScript does not know the type of this variable, you cannot treat it as having a generic parameter.

To quickly resolve this issue, eliminate the <string>:

const dbUri = config.get('dbUri');

Nevertheless, a strongly-typed solution would be more appropriate in this scenario.

The type for mongoose is likely the type imported from import mongoose from 'mongoose'. It appears you will need to obtain the typeof mongoose since the package may not export a specific type for this purpose.

Subsequently, you must type config based on its actual type. Assuming your config resembles something like:

class ConfigService {
  get<T>(prop: string): T {
    return someConfigObject[prop]
  }
}

And at some point during dependency injection, you instantiate an object of that class.

Following these steps, you can specify the type for connectDb as shown below:

import type mongooseGlobal from 'mongoose'

async function connectDb(
  mongoose: typeof mongooseGlobal,
  config: ConfigService
): Promise<void>{
  //...
}

The key takeaway here is that you must determine the type of the object you wish to pass as a parameter to a function. If an appropriate type already exists, utilize it. If not, utilize typeof to derive the type from a given value.

Playground

transferring libraries via functions in TypeScript

Answer №1

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