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    CSS is great, but isn't it tricky to namespace class names safely?

    And shouldn't there be an easy way to minify class names for production lest everyone know you named a slider class cool-slider (to avoid that naming conflict you probably invented in the back of your head).

    In short, it can be a chore to deal with CSS class names (and ID selectors), and that's been a large part of why it's hard to share modular web components that aren't just pure JavaScript. For these reasons, there should be a general-purpose name remapping tool that is easy to use and highly flexible.


    Distinguish Build Status

    Distinguish is a Node command-line tool to rename and minify identifiers in any language, isolate namespaces, and declare variables — it is designed to be simple and fast.

    In a nutshell, you put in minimal effort to mark up your CSS classes (and other identifiers), and then the program will take care of all the heavy lifting to minify names and avoid naming conflicts across modules.

    Whereas before you might write a CSS class as .search or an ID as #search, now you write ._cls-search and #_id-search. This does a few things:

    • Tells Distinguish that you are dealing with cls, a CSS class type, and id, an ID type. By keeping track, Distinguish knows which context the name search is in and can work its magic accordingly. You can define your own types to rename all sorts of things.
    • Still works in modern browsers without needing compilation (unless you have names that clash across namespaces, which are described in more detail below).
    • Uses a naming convention with an underscore and hyphen in the name selector that's easy to parse and unlikely to conflict with anything else.

    Distinguish does not require separate logic for handling CSS, HTML, JS, or any other language (like Sass, TypeScript, etc.) — rather, the name carries on its own. Distinguish by default will operate on all files in a specified source directory.

    Let's say you have an HTML file that has some CSS and JS in it.

      ._cls-content {
        border-radius: 100px;  /* so smooth */
    <div class="_cls-content" id="_id-content">Main content here</div>
      document.getElementById('_id-content').textContent = 'Injected content.';

    If you run Distinguish and specify minifying as much as possible, you'll get the following as output:

      .a {
        border-radius: 100px;  /* so smooth */
    <div class="a" id="a">Main content here</div>
      document.getElementById('a').textContent = 'Injected content.';

    That's it. No tricks or special magic. Just pure regular expression parsing and an intelligent naming module that can keep track of multiple types. And the code will execute as expected without running Distinguish so long as there are no naming collisions across modules (but more on that later).

    That's a taste of Distinguish, a renaming tool that works on any file and can be used in many different ways. But it can also do much more, like namespace directories to avoid cross-module clashing, reserve certain names, declare variables, and report unused dependencies.

    Getting started

    Try out the Distinguish command-line utility without installing anything:

    npx distinguish init

    This will create a Distinguish config file in your current directory called distinguish.config.js that looks like this:

    exports.default = {
      incrementer: 'simple', // the incrementer to use ([minimal, simple, module])
      types: ['cls', 'id'], // the types to rename (e.g. CSS classes, IDs)
      inputDir: 'src/', // the input directory to use
      outputDir: 'out/', // the output directory to use
      exclude: [], // a regular expression array describing files to exclude from renaming

    We'll dive into the options in the next section, but for now just set inputDir and outputDir to some directories you want to try out, where the input directory is some source code you want to transform, and the output directory is a clean directory where the results will be outputted.

    For a minimal example, create an index.html in your inputDir:

    ._cls-red {
      color: red;
    <div class="_cls-red">Hello world.</div>

    Now run Distinguish (if you want to watch for changes, add -w):

    npx distinguish rename

    In your output folder you should see the following:

    .red {
      color: red;
    <div class="red">Hello world.</div>

    Now try changing the incrementer to minimal in your distinguish.config.js and you should get a minimized class name of a.

    To install Distinguish globally, run:

    npm i -g distinguish

    To install Distinguish as a dev dependency in Node, run:

    npm i -D distinguish

    Config options


    Incrementers work behind the scenes to assign names. There's three main incrementers you can choose from:

    • minimal: assigns names incrementally that are as short as possible, e.g. a, b, c, ..., y, z, aa, ...

    • simple: pretty much preserve the name unless there's a naming conflict across different namespaces (see the next section for information). This is a good mode for development. If there is a conflict, _1 is appended to the end of the name, then _2 if that conflicts, and so on.

    • module: essentially the same thing as the simple mode, except the namespace is prepended to the name. If you're in a namespace called component, you may produce a class name like _cls-component_search.


    While the examples have been laser-focused on CSS classes and IDs, there's no limit to what types can be renamed. Distinguish was designed to support whatever types you want. ['cls', 'id'] is the default configuration, but you're free to modify or do away with those types.

    Distinguish will modify any string of the form _{type}-{name} that it encounters in the files it recursively crawls in the input directory, where {type} is the type name (e.g. cls). For compatibility with JavaScript variable naming rules, _{type}${name} is also transformed. For compatibility with situations where a letter must immediately follow the transformed name, _{type}-{name}_ and _{type}${name}_ are also transformed.

    For example, you could add the type fn and then have your JavaScript functions automatically minified (e.g. _fn$parse()a) — though I would recommend using an intelligent JS minifier instead.


    The exclude option in the config is an array of fully specified regular expressions for file names that you want to exclude. Note that you should use the regular expression start and end symbols (/^ ... $/) if you intend to match the whole name.

    The .namespec file

    Distinguish specially handles any files named .namespec that it encounters in its crawl. The namespec file specifies the namespace of the current directory. The namespec file can additionally import names from other namespaces, declare variables, and reserve certain names to be globally avoided in renaming.


    Namespaces provide a way to safely manage situations where you may have duplicate names that you want to treat differently in different contexts.

    An example may be the easiest way to demonstrate it.


    <link rel="stylesheet" href="toggle/toggle.css">
      ._cls-toggle {
        background: green;
    <div class="_cls-toggle"></div>
    <script src="toggle/toggle.js"></script>


    ._cls-toggle {
      background: blue;


    // Create a toggle element from scratch.
    const div = document.createElement('div');
    // Code to render it.

    In this example, there's a webpage (src/index.html) which is displaying a toggle. But it also imports CSS and JavaScript from a module called toggle which creates another toggle which coincidentally has the same class name.

    We want the sub-directory src/toggle to have its own isolated naming context, such that when we import the code into src/index.html the names do not collide and the page can ultimately output a blue toggle and a green toggle.

    Distinguish will not do anything special by default; the names will get tangled. Even though the files are in a different directory, they're in the same namespace. Let's change this by creating a namespec file in the src/toggle directory:


    namespace toggle

    Now, when we run Distinguish, all the names in the src/toggle directory (and any of its sub-directories, by default) will be treated differently. Specifically, if we compile with the minimal incrementer, _cls-toggle will map to a in the parent directory and b in the sub-directory.

    Though this example is contrived, this is a common situation in managing large web projects. Namespaces specified in a namespec file provide a lightweight means to distinguish between duplicate names in different modules.

    You may be asking why directories don't by default have different namespaces. This is because style sheets and other resources are often managed in different directories but intended to operate in the same namespace as the HTML files that depend on them. By forcing you to namespace with intention, the results are better defined.

    Anatomy of a namespace

    By default, all Distinguish projects have a namespace of root. As Distinguish recurses into sub-directories and encounters new namespaces, these are chained onto the end.

    For instance,


    namespace a

    This will endow the src/a directory with the namespace root/a.

    If there's a sub-directory b within a that has its own namespec, the chain will grow.


    namespace b

    Now, the src/a/b directory and its sub-directories will have the namespace root/a/b.


    Names can be imported across namespaces:

    namespace lib
    from barn import

    This namespec file says to look in the sub-module barn and share the classes cat, dog, and chipmunk and the ID animal-house.

    The syntax from {namespace} import will look in child namespaces by default. To look in parent namespaces or complex paths the following syntax can be used:

    • ..: look in the parent namespace
    • ../tractor: look in the parent namespace's child named tractor (i.e. a sibling namespace)
    • /: look in the root namespace. The / at the beginning means the namespace is specified as an absolute
    • farm/barn/cow: look in the namespace farm's child named barn, and then get barn's child named cow

    Imports allow controlled leakage between components. For instance, a themes namespace may share specified class names with the root namespace to be able to modify CSS classes on the main web page.

    Reserved names

    You may have a dependency which expects a certain class name or ID to be present that you have no control over (for instance, an analytics suite that expects to use a certain CSS class).

    Fret not. There's a simple mechanism to avoid clobbering these global reserved names:

    namespace lib

    Now, if you use the class _cls-analytics, it will be renamed in a way that doesn't clash. For instance, if you're using the simple incrementer, it will be renamed analytics_1.

    What if you want to specify the actual name analytics? Easy. Just write the class as analytics (remember, Distinguish only touches things that match the _{type}-{name form and its JS variant _{type}${name}).

    Reserved names affect the global naming process, so a sub-namespace that reserves a certain name will prevent the root namespace from clobbering it.

    Declaring variables

    Say you want to define a theme color that you use across the site. Technologies like Sass have been developed to allow stylesheets to use variables like this, but there's still redundancies if you need to specify the color in JavaScript, HTML, or elsewhere.

    The declare syntax in a namespec file allows you to map names automatically to single-line strings. In the following example, assume our Distinguish config file has been expanded to incorporate a type called var:

    namespace colors

    Now, we can easily access this color value in stylesheets and more.


    ._cls-foreground {
      color: _var-blue;
    ._cls-background {
      background: _var-blue;


    <svg><rect fill="_var-blue"></rect></svg>

    In this example, the color blue is mapped to the string #697f98 when _var-blue is used. This can be a very powerful mechanism to avoid redundancies across code, but it is important to note that this kind of example won't function correctly uncompiled.

    Declared variables can be imported using the imports mechanism described above.

    Unused dependencies

    If you import a name from another module and then never actually make use of that name, you may have made an error. To help you, Distinguisher will warn you about every unused dependency. These warnings will not stop the output generation.


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