A lightweight, npm-based template engine.
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Denim

A lightweight, npm-based template engine.

Installation

Install this package as a global dependency.

$ npm install -g denim

Although we generally disfavor global installs, this tool creates new projects from scratch, so you have to start somewhere...

Usage

denim can initialize any package that npm can install, including npm, GitHub, file, etc.

Invocation:

$ denim [flags] <module>

Flags:

  --help
  --version
  --prompts

Examples:

$ denim templates-module
$ denim templates-module@0.2.0
$ denim FormidableLabs/templates-module
$ denim FormidableLabs/templates-module#v0.2.0
$ denim git+ssh://git@github.com:FormidableLabs/templates-module.git
$ denim git+ssh://git@github.com:FormidableLabs/templates-module.git#v0.2.0
$ denim /FULL/PATH/TO/templates-module

Internally, denim utilizes npm pack to download (but not install) a templates package from npm, GitHub, file, etc. There is a slight performance penalty for things like local files which have to be compressed and then expanded again, but we gain the very nice benefit of allowing denim to install anything npm can in exactly the same manner that npm does.

Installing from a Relative Path on the Local Filesystem

One exception to the "install like npm does" rule is installation from the local filesystem. Internally, denim creates a temporary directory to expand the download from npm pack and executes the process in that directory, meaning that relative paths to a target modules are now incorrect.

Accordingly, if you want to simulate a relative path install, you can try something like:

# Mac / Linux
$ denim "${PWD}/../templates-module"

# Windows
$ denim "%cd%\..\templates-module"

Automating Prompts

To facilitate automation, notably testing a module by generating a project with denim and running the project's tests as part of CI, there is a special --prompts=JSON_OBJECT flag that skips the actual input prompts and injects fields straight from a JSON object.

$ denim <module> \
  --prompts'{"name":"bob","quest":"popcorn","destination":"my-project"}'

Note that all required fields must be provided in the JSON object, no defaults are used, and the init process will fail if there are any missing fields. Tip: You will need a destination value, which is added to all prompts.

Template Modules

Templates are created within a first class npm module. It could be your projects shared utilities module or a standalone template bootstrap module. The main point is creating something npm-installable that is lightweight for bootstrapping your templated projects.

A denim project is controlled with:

  • denim.js: A control file for user prompts and data.
  • templates/: A directory of templates to inflate during initialization. This directory can be configured with user prompts / data by setting the special _templatesDir variable to something different than "templates".

For example, in templates-module, we have a control file and templates as follows:

denim.js
templates/
  .babelrc
  .editorconfig
  .travis.yml
  CONTRIBUTING.md
  demo/app.jsx
  demo/index.html
  LICENSE.txt
  package.json
  README.md
  src/components/{{componentPath}}.jsx
  src/index.js
  test/client/main.js
  test/client/spec/components/{{componentPath}}.spec.jsx
  test/client/test.html
  {{_gitignore}}
  {{_npmignore}}

Templates Module Data

Packages provide data for template expansion via a denim.js file in the root of the module. The structure of the file is:

module.exports = {
  destination:  // A special prompt for output destination directory.
  prompts:      // Questions and responses for the user
  derived:      // Other fields derived from the data provided by the user
};

Note that denim requires destination output directories to not exist before writing for safety and initialization sanity.

Special Variables

There are several default data fields provided by denim that can be overridden in denim.js configuration files. A brief list:

  • Control
    • _templatesDir ("templates"): The directory root of the templates to use during inflation.
    • _templatesFilter (a noop function): A function with the signature (filePath, isIncluded) where filePath is the resolved path to a file (relative to templates dir), and isIncluded is a boolean indicating whether or not denim would ordinarily include it (e.g., it is not excluded by the .gitignore). An overriding function should return true or false based on custom logic and can optionally use the isIncluded parameter from denim's default logic.
  • File naming helpers
    • _gitignore (".gitignore")
    • _npmignore (".npmignore")
    • _npmrc (".npmrc"):
    • _eslintrc (".eslintrc")

Imports and Dependencies

The denim.js file is require-ed from a temporary extracted directory containing the full module. However, an npm install is not run in the module directory prior to starting the initialization process. This means that you can require in:

  • Files contained in the module itself.
  • Any standard node libraries. (E.g., require("path"), require("fs")).

Unfortunately, you cannot require third party libraries or things that may be found in <module>/node_modules/. (E.g., require("lodash")).

This is a good thing, because the common case is that you will need nearly none of the dependencies in denim.js prompting that are used in the module itself, so denim remains lightening quick by not needing to do any npm install-ing.

User Prompts

User prompts and responses are ingested using inquirer. The prompts field of the denim.js object can either be an array or object of inquirer question objects. For example:

module.exports = {
  // Destination directory to write files to.
  //
  // This field is deep merged and added _last_ to the prompts so that module
  // authors can add `default` values or override the default message. You
  // could further override the `validate` function, but we suggest using the
  // existing default as it checks the directory does not already exist (which
  // is enforced later in code).
  destination: {
    default: function (data) {
      // Use the early `name` prompt as the default value for our dest directory
      return data.name;
    }
  },

  prompts: [
    {
      name: "name",
      message: "What is your name?",
      validate: function (val) {
        // Validate functions return `true` if valid.
        // If invalid, return `false` or an error message.
        return !!val.trim() || "Must enter a name!";
      }
    },
    {
      name: "quest",
      message: "What is your quest?"
    }
  ]
};

denim provides a short-cut of placing the name field as the key value for a prompts object instead of an array:

module.exports = {
  prompts: {
    name: {
      message: "What is your name?",
      validate: function (val) { return !!val.trim() || "Must enter a name!"; }
    },
    quest: {
      message: "What is your quest?"
    }
  }
};

Note - Async: Inquirer has some nice features, one of which is enabling functions like validate to become async by using this.async(). For example:

name: {
  message: "What is your name?",
  validate: function (val) {
    var done = this.async();

    // Let's wait a second.
    setTimeout(function () {
      done(!!val.trim() || "Must enter a name!")
    }, 1000);
  }
}

Derived Data

Module authors may not wish to expose all data for user input. Thus, denim supports a simple bespoke scheme for taking the existing user data and adding derived fields.

The derived field of the denim.js object is an object of functions with the signature:

derived: {
  // - `data`     All existing data from user prompts.
  // - `callback` Callback of form `(error, derivedData)`
  upperName: function (data, cb) {
    // Uppercase the existing `name` data.
    cb(null, data.name.toUpperCase());
  }
}

Special Data and Scenarios

.npmignore, .gitignore

The Problem

Special files like .npmrc, .npmignore, and .gitignore in a templates/ directory are critical to the correct publishing / git lifecycle of a created project. However, publishing templates/ to npm as part of publishing the module and even initializing off of a local file path via npm pack does not work well with the basic layout of:

templates/
  .gitignore
  .npmignore
  .npmrc

The problem is that the .npmignore affects and filters out files that will be available for template use in an undesirable fashion. For example, in templates-module which has an .npmignore which includes:

demo
test
.editor*
.travis*

natural npm processes would exclude all of the following template files:

templates/.editorconfig
templates/.travis.yml
templates/test/client/main.js
templates/test/client/spec/components/{{componentPath}}.spec.jsx
templates/test/client/test.html
templates/demo/app.jsx
templates/demo/index.html

Adding even more complexity to the situation is the fact that if npm doesn't find a .npmignore on publishing or npm pack it will rename .gitignore to .npmignore.

The Solution

To address this, we have special derived values built in by default to denim. You do not need to add them to your denim.js:

  • {{_gitignore}} -> .gitignore
  • {{_npmignore}} -> .npmignore
  • {{_npmrc}} -> .npmrc
  • {{_eslintrc}} -> .eslintrc

In your module templates directory you should add any / none of these files with the following names instead of their real ones:

templates/
  {{_gitignore}}
  {{_npmignore}}
  {{_npmrc}}
  {{_eslintrc}}

As a side note for your git usage, this now means that templates/.gitignore doesn't control the templates anymore and your module's root .gitignore must appropriately ignore files in templates/ for git commits.

Templates Directory Ingestion

As a preliminary matter, templates/ is the out-of-the box templates directory default for a special prompts variable _templatesDir. You can override this in an denim.js either via prompts (allowing a user to pick a value) or derived data. Either of these approaches can choose 1+ different directories to find templates than the default templates/.

denim mostly just walks the templates directory of a module looking for any files with the following features:

  • An empty templates directory is permitted, but a non-existent one will produce an error.
  • If an <_templatesDir>/.gitignore file is found, the files matched in the templates directory will be filtered to ignore any .gitignore glob matches. This filtering is done at load time before file name template strings are expanded (in case that matters).

denim tries to intelligently determine if files in the templates directory are actually text template files with the following heuristic:

  1. Inspect the magic numbers for known text files and opportunistically the byte range of the file buffer with https://github.com/gjtorikian/isBinaryFile. If binary bytes detected, don't process.
  2. Inspect the magic numbers for known binary types with https://github.com/sindresorhus/file-type If known binary type detected, don't process.
  3. Otherwise, try to process as a template.

If this heuristic approach proves too complicated / problematic, we'll reconsider the approach.

Template Parsing

denim uses Lodash templates, with the following customizations:

  • ERB-style templates are the only supported format. The new ES-style template strings are disabled because the underlying processed code is likely to include JS code with ES templates.
  • HTML escaping by default is disabled so that we can easily process <, >, etc. symbols in JS.

The Lodash templates documentation can be found at: https://github.com/lodash/lodash/blob/master/lodash.js#L12302-L12365

And, here's a quick refresher:

Variables

var compiled = _.template("Hi <%= user %>!");
console.log(compiled({ user: "Bob" }));
// => "Hi Bob!"
var compiled = _.template(
  "Hi <%= _.map(users, function (u) { return u.toUpperCase(); }).join(\", \") %>!");
console.log(compiled({ users: ["Bob", "Sally"] }));
// => Hi BOB, SALLY!

JavaScript Interpolation

var compiled = _.template(
  "Hi <% _.each(users, function (u, i) { %>" +
    "<%- i === 0 ? '' : ', ' %>" +
    "<%- u.toUpperCase() %>" +
  "<% }); %>!");
console.log(compiled({ users: ["Bob", "Sally"] }));
// => Hi BOB, SALLY!

File Name Parsing

In addition file content, denim also interpolates and parses file names using an alternate template parsing scheme, inspired by Mustache templates. (The rationale for this is that ERB syntax is not file-system compliant on all OSes).

So, if we have data: packageName: "whiz-bang-component" and want to create a file-system path:

src/components/whiz-bang-component.jsx

The source module should contain a full file path like:

templates/src/components/{{packageName}}.jsx

denim will validate the expanded file tokens to detect clashes with other static file names provided by the generator.

Tips, Tricks, & Notes

npmrc File

If you use Private npm, or a non-standard registry, or anything leveraging a custom npmrc file, you need to set a user (~/.npmrc) or global ($PREFIX/etc/npmrc) npmrc file.

denim relies on npm pack under the hood and runs from a temporary directory completely outside of the current working directory. So, while npm info <module> or npm pack <module> would work just fine with an .npmrc file in the current working directory, denim will not.