index.ts

index.ts

// This snippet is a lazy, temporary, inappropriate, not secure fix for error:
// 
// "No 'Access-Control-Allow-Origin' header is present on the requested resource".
//
// It works as a proxy and add 'Access-Control-Allow-Origin: *' to the response header. 
// 
// 1) Init proejct and add dependencies:
// 
// ```
// npm init
// tsc --init
// npm install typescript
// npm install express
// npm install @types/express
// ```
//
// 2) Add this file.
// 
// 3) Build and start server:
// 
// ```
// tsc && node proxy.js
// ```
// 
// 4) In your frontend application, change the request to "http://localhost:8079/api/v1/books" instead 
// of "http://exmple.com/api/v1/books".

import express from 'express';
import * as request from "request-promise";

const app = express();
const port = 8079;

const bookServiceApi = 'http://exmple.com/api/v1/books'

app.use((req, res, next) => {
  // It is *DANGEROUS* to allowing all cross region access. 
  res.header('Access-Control-Allow-Origin', '*');
  next()
})

app.get('/api/v1/books', (req, res) => {
  request.get(bookServiceApi).then(experiments => res.send(experiments))
});

app.listen(port, () => console.log(`Listening on port ${port}!`));

References:

1. https://stackoverflow.com/questions/20035101/why-doesn-t-postman-get-a-no-access-control-allow-origin-header-is-present-on
2. https://medium.com/@dtkatz/3-ways-to-fix-the-cors-error-and-how-access-control-allow-origin-works-d97d55946d9