TypeError：Name.default不是构造函数

Question

I am writing a unit test for a service class called TaskService . The unit test injects a TaskService instance, whose constructor goes ahead to create a DB connection to NeDB. (i know I should mock this connection but I need to get the unit test working before I can optimise it).

task.service.ts

import {Injectable, OnDestroy} from '@angular/core';
import {Task} from "./task.model";
import Datastore from 'nedb';

@Injectable()
export class TaskService implements OnDestroy {
  private tasks: any;

  constructor(private _logger: Logger) {
    this._logger.log("Task Service Constructor");

    this.tasks = new Datastore({filename: 'db/tasks.json'});


  }

Error Message

  TypeError: nedb_1.default is not a constructor at new TaskService I:/Projects/taskmelater/src/app/tasks/shared/task.service.ts:22:18) at _createClass I:/Projects/taskmelater/node_modules/@angular/core/@angular/core.es5.js:9529:1) at _createProviderInstance$1 I:/Projects/taskmelater/node_modules/@angular/core/@angular/core.es5.js:9503:1) at resolveNgModuleDep I:/Projects/taskmelater/node_modules/@angular/core/@angular/core.es5.js:9488:1) at NgModuleRef_.webpackJsonp.../../../core/@angular/core.es5.js.NgModuleRef_.get I:/Projects/taskmelater/node_modules/@angular/core/@angular/core.es5.js:10562:1) at TestBed.webpackJsonp.../../../core/@angular/core/testing.es5.js.TestBed.get I:/Projects/taskmelater/node_modules/@angular/core/@angular/core/testing.es5.js:819:1) at Function.webpackJsonp.../../../core/@angular/core/testing.es5.js.TestBed.get I:/Projects/taskmelater/node_modules/@angular/core/@angular/core/testing.es5.js:656:1) at UserContext.<anonymous> I:/Projects/taskmelater/src/app/tasks/shared/task.service.spec.ts:20:24) at ZoneDelegate.webpackJsonp.../../../../zone.js/dist/zone.js.ZoneDelegate.invoke I:/Projects/taskmelater/node_modules/zone.js/dist/zone.js:392:1) at ProxyZoneSpec.webpackJsonp.../../../../zone.js/dist/proxy.js.ProxyZoneSpec.onInvoke I:/Projects/taskmelater/node_modules/zone.js/dist/proxy.js:79:1) 

The test runner is complaining about the this.tasks = new Datastore({filename: 'db/tasks.json'}); line.

Here is the index.js file for the NeDB package.

index.js

 var Datastore = require('./lib/datastore'); module.exports = Datastore; 

I read through a ton of similar questions but they are about a custom class that causes this error. In my case I am trying to use a non Typescript npm package in my Angular 4 application. the import statements for non typescript packages are always tricky to get right.

app.module.ts

 @NgModule({ declarations: [ AppComponent, StarterComponent, StarterHeaderComponent, StarterLeftSideComponent, StarterContentComponent, StarterFooterComponent, StarterControlSidebarComponent, TasksComponent, TaskComponent, TaskFormComponent, TaskService ], imports: [ BrowserModule, AppRoutingModule, AdminModule, AgGridModule, RouterModule, FormsModule ], providers: [TaskService, Logger], bootstrap: [AppComponent, TaskService, Logger] }) export class AppModule {} 

Questions consulted:

TypeError: xxx is not a constructor

I cannot apply the solution in this question because NeDB is an NPM package, not my own class: Error: *.default is not a constructor

Answer 1

I finished typing the question and then stumbled across this github issue: https://github.com/goatslacker/alt/issues/681

One comment states the following:

This works:

import Alt from 'alt/lib'

var alt = new Alt();

module.exports = alt;

In my case, rather than importing NeDB using import Datastore from 'nedb' , I removed the import and instead added the following to my constructor: var Datastore = require('nedb');

This solved the issue. Had to add the Datastore variable to my beforeEach function in my unit test as well.