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README.md	README.md
literally	literally
literally.png	literally.png
package.json	package.json
yarn.lock	yarn.lock

literally is a tool for literate programming in Javascript, the source code for which you are literally reading right now. Given a Markdown input file with various javascript, css, html, handlebars or block code sections throughout (such as this README.md), literally will extract, clean and generate assets for each, with a few project template formats to choose from.

It is particularly well-suited for creating literate examples for Browser libraries, and has a dedicated project template for bl.ocks, which will also generate a clean README.md from the source itself, as well as take thumbnail screenshots via puppeteer. For local development, you can switch to html format to generate debug-able Source Maps to the original Markdown. All in all, literally can generate:

.js
.js.map source maps to Markdown
.css
.html
.md cleaned Markdown
.block bl.ocks metadata
preview.png and thumbnail.png screenshots via puppeteer.

The literally "compiler" is itself an example of literate programming, and this README.md is its source. What follows begins as documentation, but gradually incorporates the implementation itself, and is organized in sections:

Installation
Development and Bootstrapping
Command Line Interface
Markdown Parsing
Javascript and Source Maps
Handlebars
Screenshots
Appendix (Utilities)
Appendix (Imports)
Appendix (Metadata)

Installation

You can add literally to your project via yarn:

yarn add literally-cli

Next, using the literally script, compile markdown to a HTML templated with the source's extracted CSS, Javascript and HTML blocks.

yarn literally my_literate_module.md

You should now have a my_literate_module.html file in your working directory, with the original markdown source's CSS, Javascript and HTML blocks inlined in their proper locations. This is the default output format, inline-html, but literally has several other output formats available via the --format flag.

Development and Bootstrapping

If you are developing/hacking on literally itself, you can build this README.md locally, using the yarn-installed copy /node_modules/literally (yes, literally is in its own package.json's "devDependencies"):

yarn build

Once built, you can run your locally-built literally compiler:

yarn literally-dev

For example, to bootstrap the compiler by compiling itself (this README.md):

yarn literally-dev --output dist --name literally --format commonjs README.md

Command Line Interface

literally uses commander for its Command Line Interface. We're looking for an API something along the lines of literally [options] [inputs...] which is exactly what literally --help describes. The commander API is quite declarative and documents itself well (though a name clash requires we pass some esoteric options):

function init_cli() {
    const pkg = get_package();
    program
        .storeOptionsAsProperties(false)
        .passCommandToAction(false)
        .version(pkg.version)
        .description(pkg.description);

    program
        .arguments("[inputs...]")
        .option(
            "-o, --output <path>",
            "The output path to write result files to"
        )
        .option(
            "-n, --name <name>",
            "The asset name (`html` and `commonjs` format only)"
        )
        .option(
            "-c, --config <path>",
            "The path for your literal config, defaults to literally.config.js"
        )
        .option(
            "-f, --format <format>",
            "Which output format to use:  block, commonjs, html."
        )
        .option(
            "-s, --screenshot",
            "Should screenshots be captured also? (`block` mode only`)"
        )
        .option("--watch", "Compile continuously")
        .action(run_compiler);

    program.parse(process.argv);
}

setTimeout(init_cli);

Options can also come from a config file - some can only come from a config file.

function load_config(cmd) {
    let {config = "literally.config.js"} = cmd;
    if (!config.startsWith("/")) {
        config = path.join(process.cwd(), config);
    }
    try {
        return require(config);
    } catch (e) {
        return {};
    }
}

An example config file in JSON format, which uses the config file only retarget parameter to map dependencies in node_modules to their JSDelivr counterparts instead:

{
    "files": ["*.md"],
    "output": "dist/",
    "format": "blocks",
    "retarget": [
        {
            "rule": "node_modules", 
            "value": "https://cdn.jsdelivr.net/npm/"
        }
    ]
}

The CLI and config file parameters are merged and then iterated over, creating compiled assets from the resulting "files":

function run_compiler(cli_files) {
    const cmd = program.opts();
    const config = load_config(cmd);
    const files = cli_files.length > 0 ? cli_files : config.files;
    const output = cmd.output || config.output || process.cwd() + "/";
    const watch = cmd.watch || config.watch;
    const format = cmd.format || config.format || "inline-html";
    const name = cmd.name || config.name;
    const screenshot = cmd.screenshot || config.screenshot;
    const retartget = config.retarget || [];
    if (!files || !(files.length > 0)) {
        console.error("No input files!");
        return;
    }

    if (!fs.existsSync(output)) {
        fs.mkdirSync(output, {recursive: true});
    }

    for (const term of files) {
        for (const file of glob.sync(path.join(process.cwd(), term))) {
            const compiler = COMPILERS[format];
            compiler(watch, file, output, name, retartget, screenshot);
        }
    }
}

These formats are availble for output:

const COMPILERS = {
    js: runwatch.bind(compile_to_js),
    html: runwatch.bind(compile_to_html),
    "inline-html": runwatch.bind(compile_to_inlinehtml),
    block: runwatch.bind(compile_to_blocks),
};

`js` Format

function compile_to_js(file, output, name) {
    const md_name = path.parse(file).name;
    const out_name = name || md_name;
    const path_prefix = path.join(output, out_name);
    const md = fs.readFileSync(file).toString();
    const {javascript, handlebars, css, sourcemap} = extract(
        md_name,
        out_name,
        md
    );

    if (javascript && javascript.length > 0) {
        write_asset(`${path_prefix}.js`, javascript || "");
        write_asset(`${path_prefix}.js.map`, sourcemap || "");
    }

    if (css && css.length > 0) {
        write_asset(`${path_prefix}.css`, css);
    }

    if (handlebars.length > 0) {
        write_asset(`${path_prefix}.handlebars`, handlebars);
    }
}

`inline-html` Format

function compile_to_inlinehtml(file, output, name) {
    const md_name = path.parse(file).name;
    const out_name = name || md_name;
    const path_prefix = path.join(output, out_name);
    const md = fs.readFileSync(file).toString();
    const {javascript, css, html} = extract(md_name, out_name, md);
    const final = template({html, javascript, css});
    write_asset(`${path_prefix}.html`, final);
}

`html` Format

function compile_to_html(file, output, name) {
    const md_name = path.parse(file).name;
    const out_name = name || md_name;
    const path_prefix = path.join(output, out_name);
    const md = fs.readFileSync(file).toString();
    let {javascript, sourcemap, css, html} = extract(md_name, out_name, md);
    if (javascript && javascript.length > 0) {
        write_asset(`${path_prefix}.js`, javascript || "");
        write_asset(`${path_prefix}.js.map`, sourcemap || "");
    }

    if (css && css.length > 0) {
        write_asset(`${path_prefix}.css`, css);
    }

    const final = template({
        html,
        src: javascript && javascript.length > 0 && `${out_name}.js`,
        href: css && css.length > 0 && `${out_name}.css`,
    });

    write_asset(`${path_prefix}.html`, final);
}

`block` Format

https://bl.ocks.org

async function compile_to_blocks(file, output, name, retarget, is_screenshot) {
    let md = fs.readFileSync(file).toString();
    for (const {rule, value} of retarget) {
        md = md.replace(new RegExp(rule, "gm"), value);
    }

    const md_name = path.parse(file).name;
    const out_name = name || md_name;
    const parsed = extract(md_name, out_name, md, true);
    const {javascript, css, html, block, markdown} = parsed;
    const final = template({
        html,
        src: javascript && javascript.length > 0 && `index.js`,
        href: css && css.length > 0 && `index.css`,
    });

    write_asset(path.join(output, "index.html"), final);

    if (block && block.length > 0) {
        write_asset(path.join(output, ".block"), block);
    }

    if (javascript && javascript.length > 0) {
        write_asset(path.join(output, "index.js"), javascript);
    }

    if (css && css.length > 0) {
        write_asset(path.join(output, "index.css"), css);
    }

    write_asset(path.join(output, "README.md"), markdown);
    if (is_screenshot) {
        await screenshot(output, out_name);
    }
}

Markdown Parsing

We'll need some helpers for dealing with markdown

function extract(md_name, out_name, src, is_blocks = false) {
    let ast = marked_ast.parse(src);
    const blocks = {markdown: "", javascript: []};

    for (const index in ast) {
        const section = ast[index];
        blocks[section.lang] = blocks[section.lang] || "";
        if (section.lang === "javascript") {
            let node;
            for (node of extract_js(blocks, md_name, section)) {
                blocks.javascript.push(node);
            }
            if (node) {
                node.add("\n");
            }
        } else if (section.type === "code") {
            blocks[section.lang] += section.code + "\n\n";
        } else if (section.type === "paragraph" && is_blocks) {
            section.text = section.text.map((x) =>
                x.replace ? x.replace(/\n/gm, " ") : x
            );
        }
        const clean_md = marked_ast_markdown.writeNode(section, index, ast);
        blocks.markdown += clean_md.trim() + "\n\n";
    }

    return extract_sourcemap(md_name, out_name, blocks);
}

Javascript and Source Maps

Javascript requires special handling to support source maps - they need the original Markdown so the generated Javascript can be annotated with it's source for debugging. The source-map module makes this pretty straightforward, though unfortunately since we do not actually parse the input Javascript, we are restricted to line granularity, which interferes somewhat with Chrome's inter-line debugging.

function extract_sourcemap(md_name, out_name, blocks) {
    const {javascript, markdown} = blocks;
    const sm = new sourceMap.SourceNode(1, 1, `${md_name}.md`, javascript);
    sm.setSourceContent(`${md_name}.md`, markdown);
    const {code, map} = sm.toStringWithSourceMap({file: `${out_name}.js`});
    const output_js = babel.transformSync(code, get_babel_options(map));
    return {
        ...blocks,
        javascript: module_template(out_name, output_js.code),
        sourcemap: JSON.stringify(output_js.map),
    };
}

function* extract_js(blocks, md_name, section) {
    let ln = blocks.markdown.split("\n").length + 1;
    for (const line of section.code.split("\n")) {
        if (line.length > 0) {
            yield new sourceMap.SourceNode(ln, 1, `${md_name}.md`, line + "\n");
        }
        ln++;
    }
}

We'd like to use babel to use features like ES-modules transparently, but without imposing our own babel config on a user's project; for this we can use 'loadPartialConfig() from the babel API.

function get_babel_options(map) {
    return Object.assign(babel.loadPartialConfig().options, {
        inputSourceMap: map,
        sourceMaps: true,
    });
}

We'll also need to manually append the sourceMappingURL trailing comment, for bl.ocks and local testing where the resulting literally JavaScript output is used directly in the browser (sans-webpack)well as set the ).

function module_template(out_name, src) {
    return `${src}\n//# sourceMappingURL=${out_name}.js.map`;
}

Handlebars

literally supports handlerbars templates and renders to either a file ${name}.handlebars when format is commonjs, or a script tag with type text/handlebars otherwise. In fact, literally itself uses such a template for its own html output formats:

<!DOCTYPE html>
<html>
    <head>
        <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
    </head>
    <body>
        {{#if html}}

        {{{indent html}}}

        {{/if}}
        {{#if css}}
        <style>
            {{{indent css}}}
        </style>
        {{/if}}
        {{#if href}}
        <link rel="stylesheet" href="{{{href}}}">
        {{/if}}
        {{#if javascript}}
        <script type="module">
            {{{indent javascript}}}
        </script>
        {{/if}}
        {{#if src}}
        <script type="module" src="{{{src}}}"></script>
        {{/if}}
    </body>
</html>

Since this is a node.js script, it can be read back into Javascript by file name. literally doesn't currently support parameterization for this name, so be sure to take into account your compiler settings - in this case the template name is literally.handlerbars and it lives parallel to the executing module. The template() function itself is created statically from the handlebars module:

function template(...args) {
    const template_path = path.join(__dirname, "literally.handlebars");
    const template_src = fs.readFileSync(template_path).toString();
    handlebars.registerHelper("indent", indent);
    return handlebars.compile(template_src)(...args);
}

The literally.handlebars template has a custom helper, indent(), which keeps blocks at the proper indentation using the parse state from handlebars. This function has to be registered with handlebars.registerHelper() to be visible to the template.

function indent(txt, data) {
    const spaces = data.loc.start.column;
    return txt
        .trim()
        .split("\n")
        .map((line) => line.padStart(line.length + spaces, " "))
        .join("\n")
        .trimStart();
}

Screenshots

The block format supports taking screenshots of your built app via puppeteer, using the --screenshot CLI flag. This feature requires peerDependencies of puppeteer and http-server; feel free to skip these if you are not planning on generating bl.ocks output.

async function screenshot(output, name) {
    const {createServer} = require("http-server");
    const sharp = require("sharp");
    const server = createServer({root: process.cwd()});
    server.listen();
    const port = server.server.address().port;
    const puppeteer = require("puppeteer");
    const browser = await puppeteer.launch();
    const page = await browser.newPage();
    await page.setViewport({width: 960, height: 500});
    await page.goto(`http://localhost:${port}/${output}/index.html`);
    //await page.waitForNavigation({waitUntil: "networkidle2"});
    await page.waitFor(1000);
    await page.screenshot({path: path.join(output, "preview.png")});
    log_asset(`preview.png`, undefined, output);
    await sharp(path.join(output, "preview.png"))
        .resize(230, 120)
        .toFile(path.join(output, "thumbnail.png"));
    log_asset(`thumbnail.png`, undefined, output);
    server.close();

    await browser.close();
}

Appendix (Utilities)

Write to disk:

const num_formatter = new Intl.NumberFormat("en-us", {
    style: "decimal",
    maximumFractionDigits: 2,
});

function log_asset(name, asset, output) {
    let size = asset
        ? Buffer.byteLength(asset, "utf8")
        : fs.statSync(path.join(output, name)).size;
    size = num_formatter.format(size / 1024);
    console.log(
        chalk`{italic literally} compiled {green ${name}}  {yellow ${size} KB}`
    );
}

function write_asset(name, asset) {
    fs.writeFileSync(name, asset);
    log_asset(name, asset);
}

Run-and-watch a compile command.

function runwatch(watch, file, ...args) {
    this(file, ...args);
    if (watch) {
        fs.watchFile(file, () => this(file, ...args));
    }
}

Re-use metadata from package.json.

function get_package() {
    const pkg_path = path.join(__dirname, "../package.json");
    return JSON.parse(fs.readFileSync(pkg_path).toString());
}

Appendix (Imports)

These node.js builtins:

const fs = require("fs");
const path = require("path");

These dependencies from package.json:

const marked_ast = require("marked-ast");
const marked_ast_markdown = require("marked-ast-markdown");
const program = require("commander");
const glob = require("glob");
const handlebars = require("handlebars");
const sourceMap = require("source-map");
const chalk = require("chalk");
const babel = require("@babel/core");

Appendix (Metadata)

license: MIT

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