JavaScript Middleware

Customise JS Middleware Overview

There are two types of customisations that can be scripted with Tyk:

1. Middleware components: These execute either pre or post validation. A pre middleware component will execute before any session validation or token validation has taken place, while a post middleware component will execute after the request has been passed through all checks and is ready to be proxied upstream.

2. Dynamic event handlers: These components fire on certain API events (see the event handlers section), these are fired Async and do not have a cooldown timer. These are documented here.

All customisations have access to a limited system API (for access to resources outside of the JavaScript Virtual Machine sandbox), however the contexts of each plugin are different and have different constraints, this API gives access to the ability to make outbound HTTP requests as well as access to the key management REST API functions.

Middleware components receive extra data (depending on their context), but all have the capability to modify the request and the session object if it has been made available to the plugin. Usage of the Session object in a middleware component is expensive as the object needs to be retrieved, and de/re-encoded multiple times as it passes through the system.

Underscore.js Library

In addition to our Tyk JavaScript API functions, you also have access to all the functions from the http://underscorejs.org/ library.

Underscore.js is a JavaScript library that provides a lot of useful functional programming helpers without extending any built-in objects. Underscore provides over 100 functions that support your favourite functional helpers:

• map
• filter
• invoke

There are also more specialised goodies, including:

• function binding
• JavaScript templating
• creating quick indexes
• deep equality testing