Typescript and Promises

promise.ts

import * as fs from 'fs';

export class Runner {

    constructor() {}

    readFile(filename: string): Promise<any | Error> {

        return new Promise((resolve, reject) => {
            fs.readFile(filename, (err, result) => {

                if(err) {

                    if (err.errno == -2) { // non existant
                        reject('File does not exist');
                    } else if (err.errno == -13) {
                        reject('I have no access to this file')
                    }

                    reject('Unknown error'); // unknown

                }

                // no errors? then we're ok!
                resolve(result);
            });
        });
    }
}

let runner: Runner = new Runner();

runner.readFile('file.txt')
    .then( result => {console.log(`file.txt -> result: ${result}`)})
    .catch(error => {console.log(`file.txt -> error: ${error}`)})

runner.readFile('no-access-file.txt')
    .then( result => {console.log(`no-access-file.txt -> result: ${result}`)})
    .catch(error => {console.log(`no-access-file.txt -> error: ${error}`)})

runner.readFile('non-existant-file.txt')
    .then( result => {console.log(`non-existant-file.txt -> result: ${result}`)})
    .catch( error => {console.log(`non-existant-file.txt -> error: ${error}`)});