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0.0.9 • Public • Published

URI Template Router

Match a URI to an RFC 6570 URI template from a set of templates.

  • Specify a list of templates to test against using {braces} to specify variables
  • Returns the best match, regardless of insertion order
  • Scales to any number of templates/patterns to test against
  • Supports repeating expressions using explode modifier
  • Routes store an associated "matchValue" argument for storing arbritrary values (including objects or functions)
  • State machine evaluation can be resumed if the returned match isn't good (e.g. if first match wasn't in the database)


var r = new Router;
r.addTemplate('http://example.com/', {}, 'index');
r.addTemplate('http://example.com/q{n}.html', {}, 'page_html');
r.addTemplate('http://example.com/q{n}.txt', {}, 'page_txt');
r.addTemplate('http://example.com/blog{/y,m,d,slug}', {}, 'blog_post');
r.addTemplate('http://example.com{/path*}', {}, 'path');
// returns:
  pattern: 'http://example.com/',
  matchValue: 'index',
  data: undefined,
// returns:
  pattern: 'http://example.com/q{n}.txt',
  matchValue: 'page_txt',
  data: { n: 'foo' },
// returns:
  pattern: 'http://example.com/q{n}.html',
  matchValue: 'page_html',
  data: { n: '123' },
// returns:
  pattern: 'http://example.com/blog{/y,m,d,slug}',
  matchValue: 'blog_post',
  params: { y: '2010', m: '01', d: '02', slug: 'inventing-the-wheel' },
// returns:
  pattern: 'http://example.com{/path*}',
  matchValue: 'path',
  params: { path: [ 'first', 'second', 'third', '' ] },



The Router class maintains a list of routes.

A Route is a URI template associated with an optional, arbitrary value.

Call Router#addTemplate to add a route to the search tree:

var router = new Router;

Variables/expressions in templates

These routes may have variables, called expressions. Expressions are put inside a matched set of curly braces:


The search routine will try to pick the template that matches the smallest set of URIs. Insertion order does not affect the outcome of the search.

Templates are automatically anchored at the beginning and end.

Naming routes

Routes may be given an optional, arbitrary value, using the third argument of Router#addTemplate(template, options, matchValue):

router.addTemplate('http://localhost/{page}.txt', {}, 'page_txt');
var result = router.resolveURI('http://localhost/index.txt');
assert(result.matchValue === 'page_txt');

Matched values

When an expression matches an input, you can see what each expression inside the template was matched to through the Result#params property:

var result = router.resolveURI('http://localhost/index.txt');
result.template === 'http://localhost/{page}.txt'
result.matchValue === 'page_txt'
assert(result.params.page === 'index');

Resume search

Functioning similar to a generator, you can call Result#next() to get the next iteration of the state machine. The next call is functional, and will return the same result each iteration (unless the tree was modified, this behavior is currently undefined).

var res2 = result.next();
assert(result.template === 'http://localhost/{page}');
assert(result.params.page === 'index.txt');

Expression types

All URI Template expressions that can be reversed should be supported:

  • {var} — percent-encoded characters are decoded into "var", stopping at reserved characters. There is no distinction between percent-encoded unreserved characters and literal unreserved characters, even though these may technically be different resources.
  • {+var} — reads value of the "var" variable without decoding
  • {#var} — consumes a leading fragment start #
  • {.var} — consumes a leading dot .
  • {/var} — consumes a leading slash /
  • {;var} — consumes a leading semicolon ;
  • {?var} — consumes a leading query start ?
  • {&var} — consumes a leading ampersand &

Some array forms are supported, where the parser will try to match multiple times, pushing each match into an array:

  • {#var+} — consumes a leading fragment start #
  • {.var+} — consumes a leading dot .
  • {/var+} — consumes a leading slash /
  • {;var+} — consumes a leading semicolon ;
  • {?var+} — consumes a leading query start ?, subsequent items consume an ampersand &
  • {&var+} — consumes a leading ampersand &

In all cases, the parser tries to match the next character in the template before reading the character into the current variable.

Repeating matches

Some types of expressions can be matched more than once and provided as array items:

var res3 = result.resolveURI('http://localhost/~root/about/me.txt');
assert(result.params.user === 'root');
assert(result.params.path[0] === 'about');
assert(result.params.path[1] === 'me.txt');


new Router()

Constructor. No options.

Router#addTemplate(pattern, options, matchValue)

  • pattern: string. Expects a valid URI Template.
  • options: object. Currently reserved.
  • matchValue: any value. User-specified arbitrary value to be returned when this route is matched. Stored in Router#matchValue and Result#matchValue.
  • returns: Route

Add a template to the set of templates. Mutates the instance.

Returns a Route object representing the particular route added.

Router#resolveURI(uri, options)

Match a given URI against the set of templates and return the best match as a Result object.

new Route(uriTemplate, options, value)


With an object params, it fills the URI Template with the given values:

var route = new Route('http://localhost/{file}.txt');
route.toString({ file: 'foo' });
// Return: "http://localhost/foo.txt"

It supports all the standard URI Template features.

Without params, generates the URI Template as a string.


Provides following properties:

  • uri: the URI that was matched
  • pattern: the pattern that was matched
  • matchValue: the value of the third argument provided to addTemplate
  • params: matched values for each of the variables, if any
  • route: The Route instance that was matched


Allows you to continue searching for a matching route. This is useful if you hit the database after the first match, but didn't find a record, so want to try the next match.

For example:

var router = new Router;
var route1 = router.resolveURI('http://localhost/index.txt');
// route1.template == 'http://localhost/{file}.txt'
var route2 = route1.next();
// route2.template == 'http://localhost/{file}'
var route3 = route2.next();
// route3 == undefined


Allows a result to be rewritten into another form using the matched data from the input. This serves a similar function to a regular expression replace.

route may be a Route object, or a string (which will create a Route object).

Returns a new Result object with the rewritten uri.

URI Template Format

URI Templates follow the RFC 6570 syntax. URI Template Router supports only the subset of syntax that can be reversed back into the original variables without data loss:

  • Variables may not be re-used.
  • The prefix modifier is treated as part of the variable name. The template <{/x:1,x}> will return values like {"x:1":"a", "x":"abc"}. Since they are separate variables, the values might not even match. For example, the URI </a/ZZ/> will return {"x:1":"a", "x":"ZZ"}.
  • The explode modifier will always type that variable as an array, and can only be used with expression modifiers with certain separators.

URI Templates in URI Template Router constist of a sequence of literal characters and/or expressions. Literal characters must appear and must be matched exactly. URI Template Router does not normalize patterns or URIs, you should perform normalization before testing a URI against the router.

Expressions start with an opening curly brace { and continue until a closing curly brace }. Expressions cannot be nested.

Expressions constist of an optional modifier, which describes how to encode the variable, and a comma-seperated list of variables. Each variable may be undefined, a key-value map, an ordered array, or a string (including blank strings).

Expression modifiers:

  • Blank modifier, indicates URL-encoding the variable
  • + Raw modifier, indicates the variable is already a URI and to not encode the variable except for invalid characters
  • / Path modifier, prefixes each variable and array item with a slash if the variable is defined
  • ? Query modifier, prefixes the first variable with ? and the remaining with &, if the variable is defined
  • & Query extension modifier, prefixes each variable and array item with & if the variable is defined

Variables are alphanumeric, and optionally end with a variable modifier:

  • The explode modifier * indicates the variable will be an array
  • The prefix modifier :n (for some positive integer n) indicates the variable is a string that has a maximum length.

Evaluation order

URI Template Router returns a single, best matching template and the values that the expressions matched.

If one template is a strict subset of another, the router tries to return the route with the smaller matching set first. In the event two patterns are disjoint, superset/subsets are computed left-to-right.

The processor evaluates the URI left to right, preferring to match templates in the following order:

  1. Matching a literal character
  2. Matching an expression prefix
  3. Matching an expression body
  4. Repeating the current variable, if marked with the explode modifier
  5. Skipping over the variable, if not marked required
  6. Skipping over the expression, if not marked required

For example, given the URI <.../foo.html>, the following templates would be preferred in the given order:

  1. <.../foo.html>
  2. <.../foo.{ext}>
  3. <.../{base}.html>
  4. <.../{file}>
  5. <...{/path}.html>
  6. <...{/path}>
  7. <...{/path*}>


  • Configurable maximum URI length
  • Blacklisted/rewrite patterns (ignore "../" segments)
  • Cast variables to numbers
  • Access to raw URI data
  • Dump error on invalid URI
  • Variable flags:
    • minimum/maximum length

Index of Files

  • README.md - you're looking at it
  • example.html - Example usage in a Web browser
  • index.js - entry point & entire code base
  • node_modules/ - packages for running tests
  • package.json - npm package metadata
  • perf.js - performance testing script
  • test/*.test.js - Mocha test suite files
  • test/base.json - Data for uri-template-router tests
  • test/uritemplate-test/ - the official URI Templates test suite


npm i uri-template-router

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