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Easily add powerful permalink or URL routing/URL rewriting capablities to any node.js project. Can be used in static site generators, build systems, web applications or anywhere you need to do path or URL transformation.


Install with npm:

$ npm install --save permalinks


Add permalinks support to any JavaScript project using node's require() system with the following lines of code:

var Permalinks = require('permalinks');
// The main export is a constructor function that must be instantiated 
var permalinks = new Permalinks();

Next, use the .format() method to generate a single permalink:

var permalink = permalinks.format(structure, file, locals);


  • structure: {String} (required) A template that determines what a permalink will look like when it's rendered (using the permalink.format() method)
  • file: {String|Object} (required) The file (object or path) for which to create the permalink
  • locals: {Object} (optional) Additional data to use for resolving placeholder values in the structure


console.log(permalinks.format('/blog/:name/index.html', 'src/about.hbs'));
//=> '/blog/about/index.html' 
console.log(permalinks.format('/archives/:name-:num.html', 'src/foo.hbs', {num: 21}));
//=> '/archives/foo-21.html' 


What is a permalink?

A permalink is a URL to a page, post or resource on your site that is intended to stay the same as long as the site exists.

Most blogging platforms and static site generators offer some level of support or plugins for generating permalinks. Typically you will see a permalink described (correctly) as an entire URL, such as

However, for most common use cases you will only need to use this library to generate the relative path portion of the URL, or /foo/index.html.

How are permalinks created?

A permalink is created by resolving the placeholder values in a [permalink structure][] (like :foo/:bar) with actual data, from locals and the parsed [file path][] (of the file for which we are generating a permalink):

// given this structure 
// and this data 
{foo: 'ONE', bar: 'TWO'}
// the resulting permalink would be 

This is covered in greater detail in the following documentation.


Create a permalink from the given structure (template), file and optional locals.


A permalink structure is a template that determines how your permalink should look after it's rendered.

Structures may contain literal strings, and/or placeholder strings like :name, which will be replaced with actual data when the format method is called.


Given a file named, we can change the aesthetics or semantics of the resulting permalink simply by changing the structure. For example:

//=> blog/10-powerful-seo-tips/ 
//=> blog/10-powerful-seo-tips.html 
//=> blog/10-powerful-seo-tips/index.html 

With a bit more information, provided as locals or from the file itself (such as, which commonly holds parsed front-matter data), we can get much more creative:

For example, if was defined as more-powerful-seo-tips, we might use it like this:

//=> blog/more-powerful-seo-tips/index.html 

We can get even more creative using helpers. We might, for example:

  • create a helper that parses a date from front-matter, such as 2017-01-02, into year, month and day
  • slugifies a title, like "Foo Bar Baz", to be dash-separated and all lower-case
  • adds the index of a file from an array of files
'/blog/:date(, "YYYY/MM/DD")/index.html'
//=> blog/:slugify(data.title)/index.html 
//=> blog/:slugify(data.title)/index.html 
//=> archives/23.html 

Your creativity is the only limitation!

Alternative syntax

Permalinks uses handlebars to resolve templates, which means that you can also/alternatively use handlebar's native mustache syntax for defining permalink structures:


Why handlebars?

There are a few reasons we decided to use Handlebars over parsing/rendering the :params internally:

  • Excellent context handling and resolution of variables. We have a lot of experience with templating, parsing and rendering. Most libraries choose the "minimalist" route for resolving :prop strings because of all the edge cases that crop up with more advanced features, and it's fast. With Handlebars, we compromise very slightly on speed (although it's still very fast) in exchange for power and reliability.
  • Helpers! You can use helpers to modify any of the variables in your permalink structure. You can even register helpers from great libraries like template-helpers or handlebars-helpers
  • Error handling: handlebars provides great error handling, but we especially like that handlebars allows us to choose what should happen when a missing helper is identified. We use that feature to detect dates and other similar patterns that might need to be parsed before calling other helpers (for example, let's say you define :month/:year/:day, but none of those variables exist. handlebars will call the helperMissing helper for each param, which gives you the opportunity to, for example, parse into an object with those properties, and return the values instead of throwing an error)
  • Other advanced handlebars features, like subexpressions and object paths (

Example using subexpressions

'/blog/{{lower (slugify data.title)}}/index.html'
// or  
'/blog/:lower((slugify data.title))/index.html'

Note that :lower( is effectively converted to {{lower, thus only the outermost subexpression will result in double parentheses. This is easier to see in the following example, which has two nested subexpressions:

'/blog/:foo((bar (baz "qux")))/index.html'

If the :param syntax seems confusing, feel free to stick with the handlebars syntax.


Type: {String|Object} (optional if locals is passed)

If a file object or string is passed, it will be parsed using node's path.parse() method, and merged with locals to create the context for resolving :props in the structure.

permalinks(structure, file, locals);
//                     ↑ 

File handling

Files may be defined as a string or an object. If defined as a string, the filepath will be converted to an object and set on the file.path property.

In other words 'a/b/' becomes { path: 'a/b/' }.


Type: (optional if file is passed)

Additional data to use for resolving :props in the structure

permalinks(structure, file, locals);
//                            ↑ 


The "context" is an in-memory object that is used to resolve placeholders in permalink structures.

The context object is created dynamically before rendering each permalinks, by merging the following objects:


If a locals object is passed as the last argument, it will be merged onto the context to be used for resolving placeholders in the permalink structure.

console.log(permalinks('/blog/:name/index.:ext', 'src/about.hbs', {ext: '.html'}));
//=> '/blog/about/index.html' 
console.log(permalinks(':category/:name/index.html', 'src/about.hbs', {category: 'blog'}));
//=> 'blog/about/index.html'



File path properties

Values on the provided file object are used to resolve placeholders in the permalink structure. File values can be overridden by locals or helpers.

A file does not need to be passed, but if a file is provided with at least a file.path property, most of the following built-in file variables will be automatically available on the context.

variable description
file.base Gets and sets base directory. Used for created relative paths. When null or undefined, it simply proxies the file.cwd property. Will always be normalized and have trailing separators removed. Throws when set to any value other than non-empty strings or null/undefined.
file.path Gets and sets the absolute pathname string or undefined. This value is always normalized and trailing separators are removed. Throws when set to any value other than a string.
file.relative Gets the result of path.relative(file.base, file.path). This is a getter and will throw if set or when file.path has not already been set.
file.dirname Gets and sets the dirname of file.path. Will always be normalized and have trailing separators removed. Throws when file.dirname is not exlicitly defined and/or file.path is not set.
file.basename Gets and sets the basename of file.path. Throws when file.basename is not exlicitly defined and/or file.path is not set.
file.stem Gets and sets stem (filename without suffix) of file.path. Throws when file.stem is not exlicitly defined and/or file.path is not set. Alias for file.stem.
file.extname Gets and sets extname property of file.path.


│                     file.path                    │
│      file.dirname     │        file.basename     │
│                       ├──────────┬─────────────┤
│                       │ │              │
│                       │ file.stem │ file.extname │
" /home/user/foo/src    /   about        .tmpl      "

A file.relative value can also be calculated if both file.base and file.path exist:

│                     file.path                    │
│      file.base        │        file.relative     │


Easily store and re-use permalink structures.

(If you're familiar with the popular blogging platform, WordPress, you might also be familiar with the built-in "Permalinks Settings" that WordPress offers. This feature attempts to replicate and improve on that functionality.)


Create a pretty preset for automatically formatting URLs, where the file.stem of a blog post is used as the folder name, followed by /index.html:

var permalinks = new Permalinks();
permalinks.preset('pretty', 'blog/:slugify(name)/index.html');
console.log(permalinks.format(':pretty', 'foo/bar/baz.hbs'));
//=> 'blog/baz/index.html' 
console.log(permalinks.format(':pretty', 'foo/bar/qux.hbs'));
//=> 'blog/qux/index.html' 


Helper functions can be used to resolve placeholders in permalink structures. For example:

// register a helper function 
permalinks.helper('foo', function() {
var url = permalinks.format(':foo', {path: 'about.hbs'});
Helper example

Use a date helper to dynamically generate paths based on the date defined in YAML front matter of a file.

var moment = require('moment');
var Permalinks = require('permalinks');
var permalinks = new Permalinks();
var file = {
  path: 'src/about.hbs',
  data: {
    date: '2017-02-14'
// "" is merged onto "this.context"  
permalinks.helper('date', function(format) {
  return moment( || 'YYYY/MM/DD');
console.log(permalinks.format(':date/:stem/index.html', file));
//=> '2017/02/14/about/index.html' 

Helpers can also optionally take arguments:

console.log(permalinks.format(':date("YYYY")/:stem/index.html', file));
//=> '2017/about/index.html' 

See the helper unit tests for more examples.

file helper

A special built-in file helper is called on every file and then removed from the context before rendering.

permalinks.helper('file', function(file, data, locals) {
  // do stuff with file, data and locals 

This is useful for modifying the context or setting properties on files before generating permalinks.

`file` helper example

Use the file helper to increment a value for pagination or something similar:

var file = new File({path: 'foo/bar/baz.hbs'});
var permalinks = new Permalinks();
var count = 0;
permalinks.helper('file', function(file, data, locals) {
  data.num = ++count;
console.log(permalinks.format(':num-:basename', file));
//=> '1-baz.hbs' 
console.log(permalinks.format(':num-:basename', file));
//=> '2-baz.hbs' 
console.log(permalinks.format(':num-:basename', file));
//=> '3-baz.hbs' 
//=> 3 



Create an instance of Permalinks with the given options


  • options {Options|String}


var permalinks = new Permalinks();
console.log(permalinks.format(':stem/index.html'), {path: 'src/about.hbs'});
//=> 'about/index.html' 


Uses parse-filepath to parse the file.path on the given file object. This method is called by the format method, but you can use it directly and pass the results as locals (the last argument) to the .format method if you need to override or modify any path segments.


  • file {Object}
  • returns {Object}


console.log(permalinks.parse({path: 'foo/bar/'}));
// { root: '', 
//   dir: 'foo/bar', 
//   base: '', 
//   ext: '.md', 
//   name: 'baz', 
//   extname: '.md', 
//   basename: '', 
//   dirname: 'foo/bar', 
//   stem: 'baz', 
//   path: 'foo/bar/', 
//   absolute: [Getter/Setter], 
//   isAbsolute: [Getter/Setter] } 


Generate a permalink by replacing :prop placeholders in the specified structure with data from the given file and locals.


  • structure {String}: Permalink structure or the name of a registered preset.
  • file {Object|String}: File object or file path string.
  • locals {Object}: Any additional data to use for resolving placeholders.
  • returns {String}


var fp = permalinks.format('blog/:stem/index.html', {path: 'src/about.hbs'});
//=> 'blog/about/index.html' 


Define a permalink preset with the given name and structure.


  • name {String}: If only the name is passed,
  • structure {String}
  • returns {Object}: Returns the Permalinks instance for chaining


permalinks.preset('blog', 'blog/:stem/index.html');
var url = permalinks.format('blog', {path: 'src/about.hbs'});
//=> 'blog/about/index.html' 


Define permalink helper name with the given fn. Helpers work like any other variable on the context, but they can optionally take any number of arguments and can be nested to build up the resulting string.


  • name {String}: Helper name
  • fn {Function}
  • returns {Object}: Returns the Permalink instance for chaining.


permalinks.helper('date', function(file, format) {
  return moment(;
var structure1 = ':date(file, "YYYY/MM/DD")/:stem/index.html';
var file1 = permalinks.format(structure1, {
  data: {date: '2017-01-01'},
  path: 'src/about.tmpl'
var structure2 = ':name(upper(stem))/index.html';
var file2 = permalinks.format(structure2, {
  data: {date: '2017-01-01'},
  path: 'src/about.tmpl'
//=> '2017/01/01/about/index.html' 
//=> '2017/01/01/about/index.html' 


Add a function for calculating the context at render time. Any number of context functions may be used, and they are called in the order in which they are defined.


  • fn {Function}: Function that takes the file being rendered and the context as arguments. The permalinks instance is exposed as this inside the function.
  • returns {Object}: Returns the instance for chaining.


permalinks.context(function(file, context) { = { title: 'My Blog' };
permalinks.helper('title', function() {
  return ||;


Normalize the given file to be a vinyl file object.


  • file {String|Object}: If file is a string, it will be converted to the file.path on a file object.
  • file {Object}
  • options {Object}
  • returns {Object}: Returns the normalize vinyl file.


var file = permalinks.normalizeFile('foo.hbs');
//=> '<File "foo.hbs">' 

Additional resources

Here is some reading material if you're interested in learning more about permalinks.


Related projects

  • handlebars: Handlebars provides the power necessary to let you build semantic templates effectively with no frustration | homepage
  • parse-filepath: Pollyfill for node.js path.parse, parses a filepath into an object. | homepage
  • vinyl: Virtual file format. | homepage


Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.

Building docs

(This project's is generated by verb, please don't edit the readme directly. Any changes to the readme must be made in the readme template.)

To generate the readme, run the following command:

$ npm install -g verbose/verb#dev verb-generate-readme && verb

Running tests

Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:

$ npm install && npm test


Jon Schlinkert


Copyright © 2017, Jon Schlinkert. Released under the MIT License.

This file was generated by verb-generate-readme, v0.4.3, on March 14, 2017.