Intercept Requests JS

☕ Code and coffee

Project

The project intercept-requests-js was born because of the necessity to redirect specific requests of third party scripts for another endpoint.

Sometimes we need to use third party tools inside our applications to improve user experience or to provide help widgets. But, most of the time we need to create an integration with those tools and we can't control what those scripts are using from the external world, such as HTTP requests etc.

With intercept-requests-js you can intercept specific requests by domain, by keyword and in a near future with regex. When you intercept a http request, you can redirect it, change headers, change body, or anything else that you want before your browser sends it.

How to use

Install

Install intercept-requests-js with npm:

$ npm i --save intercept-requests-js

Or using yarn:

$ yarn add intercept-requests-js

Configuration

This module will provide an InterceptRequestsJs function and ListItem that is the type of configuration item. You just need to create your Array<ListItem> and pass it to the InterceptRequestsJs function like this.

import { InterceptRequestsJs, ListItem } from 'intercept-requests-js';

const listItems: ListItem[] = [
  {
    listening: 'yahoo',
    ignore: [],
    executeWhenOpen: (context: XMLHttpRequest, args: (string | boolean)[]) => {
      return { objectRequest: context, newArguments: args };
    },
    executeBeforeSend: (context: XMLHttpRequest, args: (string | boolean)[]) => {
      return { objectRequest: context, newArguments: args };
    },
  },
];

InterceptRequestsJs(listItems);

Now, when any request matches with any listening property of Array<ListItem>, the methods executeWhenOpen and executeBeforeSend will be called before browser dispatches it, so if you need to change something on an intercepted request, do it in your methods. For example, let's suppose that one widget/script is using some yahoo service and I want to redirect this search for google, I can do it like this:

// Intercept all requests that contain yahoo in your domain and redirect to google:
import { InterceptRequestsJS, ListItem } from 'intercept-requests-js';

const executeWhenOpen = (context: XMLHttpRequest, args: (string | boolean)[]) => {
  const newArguments = ['GET', 'http://google.com', args[2]];

  return { objectRequest: context, newArguments };
};

const listItems: ListItem[] = [
  {
    listening: 'yahoo',
    ignore: [],
    executeWhenOpen: (context: XMLHttpRequest, args: (string | boolean)[]) => executeWhenOpen,
  },
];
InterceptRequestsJs(listItems);

Obviously it isn't the best example, we can't change the contract of return that script is waiting, because it can break the application and we don't want this to happen. But, let me show you a real example:

Real usecase

Before start, for reasons of ethic I'll call the name of third party product as help widget.

At one of my last jobs, we were using help widget to share articles with our users, and although help widget is an awesome product we had some problems with latency, down API etc., and it impacted our users and our attendance teams. So, we didn’t have time and it didn't make sense at that moment to build our own widget. We decided to create a microservice that receives the help widget requests and keep in cache the responses to guarantee that the content will be shown for our users. Basically, we create one layer inside our infrastructure to receive help widget requests, send this request to help widget API from our back end and save in cache the response. It has been about 3 years that this product is running without any problems and gets around 28 million views every month.

Without Intercept Requests JS

With Intercept Requests JS

Describe types

Property	Type	Description	Optional
listening	string	Name of domain, keyword, etc that we can get specific request	false
ignore	string[]	List of words that we should ignore if url include	false
executeWhenOpen	(context: XMLHttpRequest, args: (string|boolean)[])	context is the current request, args are the current arguments passed to request	false
executeBeforeSend	(context: XMLHttpRequest, args: (string|boolean)[])	context is the current request, args are the current arguments passed to request	true

Caution!

The methods executeWhenOpen and executeBeforeSend receive args parameter and the values needs to follow this sequency:

executeWhenOpen: ['http method', 'URL'] For more information see the page of XMLHttpRequest.open

executeBeforeSend: ['body'] For more information see the page of XMLHttpRequest.send

Examples

• Simple Redirect
• Change Body
• Change Headers
• Change Method
• Concat URLs

Next steps

• Enable Regex.
• Provide a method to change API response value.

How to contribute

• Make a fork bases in this repository
• Create a new branch git checkout -b my-feature
• Commit your changes yarn commit
• Push your changes git push origin my-feature

After the merge of your pull request is done, you can delete your branch

📝 License

This project is based on the MIT License. See the file LICENSE for more informations.