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Hijacker is a develoment too meant to proxy to an existing API while being able to mock and modify specific requests via rules.

Get Started



npm i -D @hijacker/core


npm i -g @hijacker/core

Create Config

Create config file named hijacker.config.js with the following:

module.exports = {
  port: 3000,
  baseRule: {
    baseUrl: '<YOUR_API_URL>'
  rules: []

View Config for more information.


Add a hijacker script to your package.json file: "hijacker": "hijacker".

Then run the following command in the directory with your config file:

npm run hijacker

Your hijacker instance should now be running at http://localhost:3000 with the interface available at http://localhost:3000/hijacker.



Property Descripton Type Required Default
port Port that you want the hijacker instance to run on number yes
baseRule Base rule that other rules will inhert from. See Base Rule Partial<Rule> yes
rules Array of hijacker rules. See Rule Partial<Rule>[] yes
logger Logger configuration options. See Logger LoggerOptions no


A tells hijacker how to handle certain requests. If no matching rule is found, hijacker will proxy the request to the API server.

Property Description Type Required Default
name Rule name. Used for display purposes only string no
disabled If rule is disabled it can't be matched boolean no false
type Rule type. Used to determine which RuleType to use for matching and handling the request string rest
baseUrl Base URL for API you want to point hijacker at for specific rule string no

Base Rule

The base rule allows you set default values for the

Rule Types

By default hijacker includes Rest and a GraphQL rule types. Each rule type can have additional properties that build upon the base rule properties. Each rule will be merged with the Base Rule and use it's values unless overridden in the rule.

The base rule has the same values as Rules. The only difference is that baseUrl is required so that requests that have no matching rule will be able to be proxied.

Rest Rule

The rest rule type is meant for REST APIs, and will be used for rule's where type is set to rest. The rest rule type has the same properties as the Rule, as well as the following:

Property Description Type Required Default
skipApi boolean no false
method HTTP method of the request to match on. GET | HEAD | POST | PUT | DELETE | OPTIONS | TRACE | PATCH | ALL no ALL
body Response body to send back when a rule matches any no undefined
path URL path of request to match on. string yes
statusCode Status code you would like hijacker return for a request number no
routeTo Path to redirect request to at the API url string no

GraphQL Rule

The GraphQL rule type expands on the Rest Rule but adds matching that works for GraphQL queries. Right now the GraphQL rule type only matches on the operation name.

Property Description Type Required Default
operationName Operation to match in graphql query string yes


query TestQuery {
  posts {

For the above query, TestQuery is the operationName that should be used to match query in a rule.


Settings for built in logger. This may eventually get changed to accepting a custom logger.

Property Description Type Required Default
level Max log level that you wan't logged to the console. SILLY | DEBUG | HTTP | INFO | WARN | ERROR | NONE no INFO

Extending Hijacker

Hijacker was made with extensibility in mind. There are a two ways Hijacker can be extended: custom rule types and hooks.


Plugins are how hooks and rule types are packaged up to be added to a config for a hijacker user to use.

Property Description Type Required Default
name Name of plugin string yes
initPlugin Function called to initialize plugin and pass HijackerContext (context: HijackerContext) => void no
hooks Array of hook names that the plugin allows to be hooked into string[] no
handlers List of hook handlers for plugin Record<string, function> no
ruleTypes Array of custom rule types RuleType[] no

Custom Rule Types

It is possible to create custom rule types, that allow for request matching and handling. You can view RestRule and GraphqlRule for examples.

Property Description Type Required Default
type Rule type used to match rules string yes
createRule Create rule object used for the handler (rule: Partial<Rule<T>>) => Rule<T> yes
isMatch Used to determine if request matches a rule (request: HijackerRequest, rule: Rule<T>) => boolean yes
handler Request handler for rule type (request: Request<T>, baseRule: Partial<Rule<T>>, context: HijackerContext) => Promise<HijackerResponse> yes


Hooks allow plugins to listen and modify objects at specific points in the request lifecycle. Hook handlers are passed an object that they can modify and return an object of the same shape. Right now Hijacker has hooks for the following events:

Hook Name Type Description Synchronous
HIJACKER_START Config Executed when hijacker starts up and allows modifying the hijacker config yes
HIJACKER_REQUEST HijackerRequst Begining of request. Called before rule matched no
HIJACKER_RESPONSE HijackerResponse Called after request handler, before response returned to client no

Plugins are able to add additional hooks using the HookManager which allow other plugins to modify their functionality.