field-trip

field-trip

walk a directed graph async without knowing its structure ahead of time

Background

There are plenty of modules for traversing

• file systems
• arrays
• trees

so long as their structure is known ahead of time. What if you require the asynchronous process of visiting a node in order to learn of its children?

Usage

Let's take a field trip through a tree, pretending to be ignorant of its structure up front:

var fieldtrip = require('field-trip')

var db = {}
db[0] = {key: 0, value: 1, kids: []}
db[1] = {key: 1, value: 2, kids: [0]}
db[2] = {key: 2, value: 3, kids: [4]}
db[3] = {key: 3, value: 4, kids: [2]}
db[4] = {key: 4, value: -1, kids: [0, 1]}

// Begin taking a field trip through this unknown structure!
fieldtrip([3], visit, function () {
  console.log('all done')
})

// Visit a single node. 'add' to add children; 'done' when finished visting.
function visit (key, add, done) {
  lookupKey(key, function (err, node) {
    if (err) return done(err)

    console.log('KEY', key, 'VALUE', node.value)

    node.kids.forEach(add)

    done()
  })
}

// Look up a key through some intensive asynchronous process.
function lookupKey (key, cb) {
  setTimeout(function () {
    cb(null, db[key])
  }, Math.floor(Math.random() * 100))
}

This will output

KEY 3 VALUE 4
KEY 2 VALUE 3
KEY 4 VALUE -1
KEY 0 VALUE 1
KEY 1 VALUE 2
KEY 0 VALUE 1
all done

API

var fieldtrip = require('field-trip')

fieldtrip(origins, visit, finish)

Calls the function visit on each element in the array origins.

Each call to visit expects the signature function (node, add, done), where add can be called with another node to visit, and done MUST be called to signal that this node's visitation has completed. Call done(err) to signal an error and end the traversal.

finish is called when either all nodes have been visited, or an error has occurred.

Install

With npm installed, run

$ npm install field-trip

Thanks!

Thanks to chrisdickenson's walk-dag module, which was the closest I could find to this. Example and tests are mostly stolen from his work. :)

License

ISC