Magic Bridge

Magic Bridge lets you call functions on a Node.JS server from a client, abstracting away HTTP.

Register a function on the server:

const newBridge = require('@magic-bridge/bridge')
// import bridge from '@magic-bridge/bridge'
const bridge = newBridge()

// register functions (or classes)
bridge.register(function getServerThing() {
  return 'i am a string from server'
}

// use with express 
const app = express()
app.use('/jsonrpc/default', bridge.middleware())

Now you can call it from the client:

const bridge = require('@magic-bridge/client')
// import bridge from '@magic-bridge/client'
const bridge = newBridge()

// call a function on the server!
const thingFromServer = await bridge.getServerThing()
// thingFromServer === 'i am a string from server'

Install

At your server:

npm install @magic-bridge/bridge

At your client:

npm install @magic-bridge/client

Usage

• Create a bridge instance
• Registering functions
  • Just a function
  • A function with context
  • A function with a given name
  • A function with a given name and context
  • An instance of a class
  • A plain object
• Using middleware with Express
• Multple bridges
• Local arg resolvers

Create a bridge instance

The Magic Bridge module exports a factory function for making new bridges both on the client and the server. The server optionally accepts some advanced options:

On the server

const newBridge = require('@magic-bridge/bridge')

const bridge = newBridge()
// or
const bridge = newBridge(opts)

Option	Description	Type	Default
ignoreMethodNameRegex	Functions registered that match this regex will be ignored. Such as methods on a class starting with an underscore to denote that they are private	regex	/^_/
throwOnDup	Will throw an error if more than one function is added with the same name	boolean	true

On the client

The client accepts one optional arguemnt; the url/path of the Magic Bridge middleware

const newBridge = require('@magic-bridge/client')

const bridge = newBridge() // uses /jsonrpc/default
// or 
const bridge = newBridge('/my-magic-bridge-url')

the client bridge is now ready to call functions on the server:

// bridge calls must always be async
const thingFromServer = await bridge.doServerThing()

Registering functions

Magic Bridge provides a few ways of registering functions via register():

Just a function

bridge.register(function func() { ... })
// client: await bridge.func()

A function with context

const obj = {
  x: 99,
  func: function () { 
    return this.x
  }
}
bridge.register(obj.func, obj)
// client: await bridge.func() --> 99

A function with a given name

bridge.register('myFunc', () => { ... })
// client: await bridge.myFunc()

A function with a given name and context

const obj = {
  x: 99,
  func: function() { 
    return this.x
  }
}
bridge.register('myFunc', obj.func, obj)
// client: await bridge.myFunc() --> 99

An instance of a class

This is quite handy, espcially in combination with multiple bridges

class Clazz {
  myMethod() {
    return 99
  }
  anotherMethod() {
    return 88
  }
}
const clazz = new Clazz()
bridge.register(clazz)
// client: await bridge.myMethod() --> 99
// client: await bridge.anotherMethod() --> 88

Functions on a plain object

This is quite handy, espcially in combination with multiple bridges

const obj {
  myFunction() {
    return 99
  }
  anotherFunction() {
    return 88
  }
}

bridge.register(obj)
// client: await bridge.myFunction() --> 99
// client: await bridge.anotherFunction() --> 88

Using middleware with Express

Magic Bridge is designed to be used as Express middleware. The default path used by the client is /jsonrpc/default, so the default set up is to do this:

const app = express()
app.use('/jsonrpc/default', bridge.middleware())

If you do use a different path, you must also configure the bridge side on the client to use it:

// client side:
const bridge = newBridge('/my-magic-bridge-path')

Multple bridges

You can create multiple bridge instances in a single application, this useful for two main reasons:

1. It acts as a namespace for classes or collections of related functions
2. Registered functions/methods requiring different credentials can be used as separate middleware

const newBridge = require('@magic-bridge/bridge')

const auth = new Auth();
const account = new Account()

const authBridge = newBridge()
const accountBridge = newBridge()

app.use('/jsonrpc/auth', authBridge.middleware())
app.use('/jsonrpc/account', ensureLoggedIn(), accountBridge.middleware())

and on the client:

const newBridge = require('@magic-bridge/client')

const authBridge = newBridge('/jsonrpc/auth')
const accountBridge = newBridge('/jsonrpc/account')

await authBridge.login()
await accountBridge.changeUsername()

Local arg resolvers

Functions on the server can be injected with request, response, request.session and request.cookie arguments that are invisible to the client.

Use arguments with these method names in any postion to have them injected:

Argument	Resolves to
_request_	The (express) request object
_response_	The (express) response object
_session_	The (express) request session object (if using express-session middleware
_cookies_	Parsed request cookies

Examples:

function changeUsername(_session_, newUsername) {
  const user = db.getUser(_session_.userId)
  user.setUsername(newUsername)
  ...
}

function changeUsername(newUsername, _cookies_) {
  const user = db.getUser(_cookies_.token)
  user.setUsername(newUsername)
  ...
}

Credits

Magic Bridge is inspired by JSON-RPC-Java (later renamed Jabsorb) a library I used circa 2006-8 to do Ajaxy stuff.

Magic bridge partially implements the JSON-RPC 2.0 specification (it doesn't do batches)