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A minimal framework for creating WebPipe blocks (and eventually triggers).


The Block API does 3 things for you:

  • Declare the block metadata like name, description, inputs, and outputs.
  • Provide a function (either synchronous or asynchronous) that implements the block.
  • Start an HTTP server on a specified port, or get a handler for use with a Node.js HTTP server or framework.

The server will automatically handle the WebPipe's OPTIONS request, and parsing/serializing the inputs/outputs before invoking your handler function.


There are three ways to declare the metadata and handler function.

Use the chaining API:

block = new Block()
  .name("Square Root")
  .description("Calculates the Square Root of a number.")
  .input("radicand", "number", "The number we want to find square root for.")
  .output("square_root", "number", "The square root.");

Pass a function to the constructor, which binds the new object to "this" inside the function. This works great with CoffeeScript:

block = new Block ->
  @name "Square Root"
  @description "Calculates the Square Root of a number."
  @input "radicand", "number", "The number we want to find square root for."
  @output "square_root", "number", "The square root."

Pass a standard WebPipe "Block" descriptor to the constructor:

block = new Block({
  "name": "Square Root",
  "description": "Calculates the Square Root of a number.",
  "inputs": [{
    "name": "radicand",
    "type": "number",
    "description": "The square root."
  "outputs": [{
    "name": "square_root",
    "type": "number",
    "description": "The square root."


A handler with an inputs argument is added to the block using the handle method:

block.handle(function(inputs) {
  return {
    square_root: Math.sqrt(inputs.radicand)

In this case the return value is used as the outputs object.

Declare the second callback argument to put the block in asynchronous mode. Pass the outputs object to the callback when it's done:

block.handle(function(inputs, callback) {
  setTimeout(function() {
      square_root: Math.sqrt(inputs.radicand)
  }, 1000);


You can start a simple webserver on the specified port using the listen method:


If the port number is omitted it will check process.env for the PORT key, or use 3000 by default:


You can also get a Node.js HTTP server compatible request handler. This is equivalent to the above examples: