node package manager
Loosely couple your services. Use Orgs to version and reuse your code. Create a free org »



A simple, powerful library for generalized hierarchical path-routing for client-side and server-side applications. grapetree-core powers the grapetree url routing library and was inspired by cherrytree. Like crossroads.js, router.js, and cherrytree, grapetree-core embraces the single-responsibility principle and is entirely stand-alone, free of any dependencies on a framework of any kind.


  • Intuitive nested routing description
  • Route lifecycle hooks so each part of the path can have a setup and cleanup function
  • Familiar error bubbling (errors bubble to the nearest handler up the tree)
  • Small footprint (< 14.5 KB unminified uncompressed)


npm install grapetree-core


var GrapeTreeCore = require('grapetree-core')

GrapeTreeCore(routeDefinition) - Returns a new router instance based on routeDefinition, which should be a function that gets a Route object as its this context.

GrapeTreeCore.param - Special value used by Route.route - see below.

GrapeTreeCore.Future - A reference to the async-future module, which grapetree-core uses internally. This does not have to be the futures/promises implementation you use to return a future from enter and exit handlers, but a future must have a then, catch, and finally method.

Router objects

router.go(newPath[, emitChangeEvent][, softQueue]) - Changes the current path and triggers the router to fire all the appropriate handlers. Returns a future that is resolved when the route is complete or has an error that isn't handled by a Route's error handler.

  • newPath - The path to change to
  • emitChangeEvent - (default true) Whether to emit the "change" event
  • softQueue - (default true) If true, causes the path to only be executed if it's the last one in the queue (and be discarded otherwise). If false, every queued path is handled in order.

router.cur - gets the current path (transformed if a transform is being used).

router.transformPath(trasformFns) - Sets up path transformation, which modifies the internal path before passing it as an argument to the "change" event and Route.default handlers and after getting an external path from the router.go and Route.route functions. This is mostly used for libraries that want to extend grapetree-core (like grapetree itself). Transform functions can be passed both full paths and path segements.

  • trasformFns - an object like {toExternal: function(internalPath){...}, toInternal: function(externalPath){...}}

router.on - router inherits from EventEmitter and so gets all the methods from it like router.once and router.removeListener. This can throw an exception if no Route error handlers catch an exception.

router.currentPath - the current path loaded in the router.

Router events

  • 'change' - Emitted after all the handlers for a particular new path have been run. This is the only event. The event data contains the new path.

Route objects

this.route(pathSegment, routeDefinition) - creates a sub-path route. The routes are tested for a match in the order they are called - only one will be used.

  • pathSegment - the parts of the path to match a route path against (e.g. ['a','b'] or 'x'). If pathSegment is an array, the route only matches if each item in pathSegment matches the corresponding parts in the path being changed to. If pathSegment is not an array, it is treated as [pathSegment]. If any of the items in the array are GrapeTreeCore.param, matching parts of the path being changed to are treated as parameters that will be passed to the routeDefinition function.
  • routeDefinition - a function that gets a Route object as its this context. It is passed any parameters that exist in pathSegment in the same order.

this.default(routeDefinition) - creates a default sub-path route that is matched if no other route is. The routeDefinition function is passed the full sub-route (ie if the default is within ['a','b'] and the path is ['a','b','c','d'], default will get ['c','d'])

this.redirect(newPath[, emitOldPath=false]) - Changes the route to be loaded only if no subroute matches. If a subroute matches, the redirect is ignored.

  • newPath - the new route

  • emitOldPath - if true, the 'change' event will be triggered with the original path

  • routeDefinition - a function that gets a Route object as its this context. It is passed the new pathSegment being changed to. If router.transformPath has been called, the parameter will have been transformed with the transform.

this.enter(handler) - sets up a handler that is called when a path newly "enters" the subroute (see Route Lifecycle Hooks for details).

  • handler(parentValue) - a function that will be called when the path is "entered". The handler may return a future, which will be waited on before child enter-handlers are called.
    • parentValue is the value of the future returned by its parent's enter handler, or undefined if no future was returned by its parent.

this.exit(handler) - sets up a handler that is called when a new path "exits" the subroute (see Route Lifecycle Hooks for details).

  • handler(parentValue, divergenceDistance) - a function that will be called when the path is "exited". The handler may return a future, which will be waited on before parent exit-handlers are called.
    • parentValue is the value of the future returned by its parent's enter handler (not its parent's or child's exit handler), or undefined if no future was returned by its parent.
    • divergenceDistance is the number of routes between it and the recent path-change (e.g. for a change from ['a','b','c','d'] to ['a','b','x','y'], c's divergence distance is 0, and d's is 1). This is useful, for example, if some work your exit handler does is unnecessary if its parent route's exit handler is called.

this.error(errorHandler) - Sets up an error handler that is passed errors that happen anywhere in the router. If an error handler is not defined for a particular subroute, the error will be passed to its parent. If an error bubbles to the top, the error is thrown from the router.go function itself. The handler may return a future, which will propogate errors from that future to the next error handler up, if that future resolves to an error.

  • errorHandler(error, info) - A function that handles the error. The second parameter is an object with info about where the error happened. It has the following members:
    • info.stage - the stage of path-changing the error happened in. stage can be either "enter", "exit", or "route"
    • info.location - the path segement (relative to the current route) where the error happened ([] indicates the current route)

Route Lifecycle Hooks

Handler order

  1. 'change' event handler
  2. Exit handlers - from outermost to the divergence route (the route who's parent still matches the new route)
  3. Enter handlers - from the convergence route (the route matching the first segement of the new path) to the outermost new route


The routing hooks in grapetree-core are simple but powerful. Basically exit handlers are called from leaf-node routes inward, and enter handlers are called outward toward the leaf-nodes.

var router = Router(function() { // root 
    this.route('a', function() {
     this.enter(function() {
        // entering a 
        this.exit(function() {
         // exiting a 
        this.route('x', function() {
            this.enter(function() {
                // entering x 
            this.exit(function() {
                // exiting x 
    this.route('b', function() {
     this.enter(function() {
         // entering b 
        this.exit(function() {
         // exiting b 
router.on('change', function(newPath) {
    console.log('went to '+newPath.join(','))
router.go(['a', 'x']).then(function() {
    return router.go(['b'])

The order the handlers are called in the above example is:

  1. change event: "went to a,x"
  2. entering a
  3. entering x
  4. change event: "went to b"
  5. exiting x
  6. exiting a
  7. entering b

Error Handling

Error handling in grape-tree is an attempt to be as intuitive as possible, but they are a bit different from traditional try-catch, because the success of a parent route should not depend on the success of a child route (as opposed to normal try-catch situations where the calling code's success depends on the called code). Here are some facts about how errors are handled:

  • If a child route has an error and it bubbles up past its parent, its parent is not actually affected - all its enter and exit handlers are called as normal.
  • Errors bubble up from the route where they happened, to the error handler of nearest ancestor route that has one.
  • If a route has an error, the path will be incomplete (e.g. if you try to go to /a/b/c/d and there was an error at c, the path will end up bing /a/b)

See the unit tests for exhaustive examples of how error handling works. For the most part, you should be able to use it well without fully understanding the intricacies of how it works.

Default Handlers

Like the error handlers, default handlers for a route also cover the scope of that route's children. In other words, if a child doesn't have a default route, its parent's (or grandparent's etc) default route will be used. This allows you to have a single default handlers at the top level that will catch any invalid route.


  • implement a way to match on arbitrary paths (like putting a function in for hte path so you can say "i matched 4 tokens on the path"

  • If an error happens in a enter handler and is not handled by an error handler in that route, enter handlers of parents should probably continue to run

    • if a parent doesn't handle the error either, should its exit handler be automatically called?
  • Browser testing


  • 3.1.3 - minor
  • 3.1.2 - fixed bug where default wasn't being called again if it went back to a route it was previously at (but wasn't most recently at) - there's a test in the unit tests for this
  • 3.1.1 - Fixing bug where default didn't work properly when two defaults in a row are routed to
  • 3.1.0 - Adding cur property
  • 3.0.0 - BREAKING CHANGE - adding softqueue and making it default
  • 2.4.2 - fixing redirect so that it can coexist with default
  • 2.4.1 - fixing the return value of go when something queues
  • 2.4.0 - Changing behavior so that if 'go' is called while a previous 'go' is still in progress, it queues up the next go to execute after the current one finishes
  • 2.3.1 - fixing bug where routing after an error has propogated all the way up was routing wrong
  • 2.3.0 - Breaking Changes
    • adding redirect functionality
    • removing leafDistance from enter handler
    • change event now doesn't care if part of the route failed, it will always send the event with the full path requested
  • 2.2.0 - making a route's default handlers get run in the case a route's children don't have deafult routes
  • 2.1.0 - changing exit handlers so they get both a "value" and the divergenceIndex (just like the enter handler gets two similar parameters)
  • 2.0.1 - fixing bug with switching between paths that have the same beggining in a route with multiple parts
  • 2.0.0 - major API change
    • changing the "go" event to be the "change" event
    • getting rid of enter and exit "levels"
    • adding the ability to return a future from enter and exit handlers, which will cause child enter handlers to only run when those resolve and handle errors that come out of the futures properly
    • adding the ability to return a future from error handlers, which if resolve to an error will propogate to the next error handler up
  • 1.1.1 - minor error reporting fix
  • 1.1.0
    • improving exception message
    • fixing default's path to be a path segement instead of the full path
    • fixing up error handling to behave more reasonably, and adding documentation about how error handling works specifically
    • changing order of the error handler's arguments
  • 1.0.0 - changing the transformPath method to allow transforms in both directions
  • 0.0.3 - pass the leaf distance to the first enter handler
  • 0.0.2 - pass the divergence/convergence distance to the first enter/exit handler
  • 0.0.1 - first version

How to Contribute!

Anything helps:

  • Creating issues (aka tickets/bugs/etc). Please feel free to use issues to report bugs, request features, and discuss changes
  • Updating the documentation: ie this readme file. Be bold! Help create amazing documentation!
  • Submitting pull requests.

How to submit pull requests:

  1. Please create an issue and get my input before spending too much time creating a feature. Work with me to ensure your feature or addition is optimal and fits with the purpose of the project.
  2. Fork the repository
  3. clone your forked repo onto your machine and run npm install at its root
  4. If you're gonna work on multiple separate things, its best to create a separate branch for each of them
  5. edit!
  6. If it's a code change, please add to the unit tests (at test/grapetreeCoreTest.js) to verify that your change
  7. When you're done, run the unit tests and ensure they all pass
  8. Commit and push your changes
  9. Submit a pull request:


Released under the MIT license: