javascript - Error with Inheritance and TypeScript: X is not a constructor function type -

i working on small webapp , using typescript, node.js, express, , mongodb.

i have super class want 2 other classes inherit from. classes listed below. when compile, 2 classes trying inherit complain superclass (the give same error): "[class file path (in case a)] not constructor function type"

a.ts

export class {     //private fields...      constructor(username: string, password: string, firstname: string,         lastname: string, accounttype: string)      {         // initialisation     } } 

b.ts

import = require('./a); export class b extends {     constructor(username: string, password: string, firstname: string,         lastname: string, accounttype: string)      {         super(username, password, firstname, lastname, accounttype);     } } 

c.ts

import = require('./a ); export class c extends {     constructor(username: string, password: string, firstname: string,         lastname: string, accounttype: string)      {         super(username, password, firstname, lastname, accounttype);     } } 

this pretty simple, , yet class c , b cannot compile. examples have seen online not have other syntax writing these classes/ constructor. trying follow convention, can't seem work.

any appreciated! reading.

replace

import = require('./a'); 

with

import { } './a'; 

or

import modulea = require('./a');  export class b extends modulea.a {   // ... }