How to use npm library in NestJs

Question

I'm new into NestJs and I've been trying to use the mathjs library inside a custom decorator in order to verify that a string is a valid unit of measurement (would also appreciate guidance on this) but I've been getting the following error, and I'm guessing I don't understand how to correctly use a 3rd party library

TypeError: Cannot read properties of undefined (reading 'unit')
    at Object.validate (D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\src\validation\is-measurement-unit.ts:14:28)    at CustomConstraint.validate (D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\node_modules\src\register-decorator.ts:63:26)
    at D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\node_modules\src\validation\ValidationExecutor.ts:271:68     
    at Array.forEach (<anonymous>)
    at D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\node_modules\src\validation\ValidationExecutor.ts:253:82     
    at Array.forEach (<anonymous>)
    at ValidationExecutor.customValidations (D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\node_modules\src\validation\ValidationExecutor.ts:252:15)
    at ValidationExecutor.performValidations (D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\node_modules\src\validation\ValidationExecutor.ts:212:10)
    at D:\Documentos\Camilo\Mercadonde\pricesmart_api_proxy\node_modules\src\validation\ValidationExecutor.ts:114:14     
    at Array.forEach (<anonymous>)

Here is my code so far

import { ValidationArguments, registerDecorator } from 'class-validator';
import math from 'mathjs';

export function IsMeasurementUnit() {
  return function (object: Object, propertyName: string) {
    registerDecorator({
      name: 'isMeasurementUnit',
      target: object.constructor,
      propertyName: propertyName,
      constraints: [],
      options: { message: 'Text must be a unit of measurement' },
      validator: {
        async validate(value: any, args: ValidationArguments) {
          console.log(math.unit(45, 'cm'));
          console.log(value);
          return true;
        },
      },
    });
  };
}

I've also checked the custom provider solution, but it seems like over engineering, is there an easiest way?

Answer 1

the runtime is nodejs. So you can use any nodejs package in nestjs apps.

The issue you're facing is with typescript, not nestjs.

You can do: import * as math from 'mathjs'; or enable the allowSyntheticDefaultImports compiler option.