html-loader

What is html-loader?

The html-loader npm package is used to export HTML as string. When used with webpack, it allows you to require HTML files as modules. It can also minimize the HTML when the webpack 'minimize' option is enabled. It's useful for processing HTML files to include them as part of your JavaScript bundle.

What are html-loader's main functionalities?

Export HTML as String

Allows you to use HTML files as modules by exporting them as strings. This can be useful when you want to include your HTML in your JavaScript files.

require('html-loader!./file.html')

Interpolate Custom Syntax

Enables interpolation with a custom syntax within the HTML file. This is useful for including images or other assets using a require statement.

require('html-loader?interpolate=require!./file.html')

Minimize HTML

When used with webpack, you can minimize the HTML by setting the 'minimize' option to true. This helps reduce the size of the HTML included in your JavaScript bundle.

module.exports = { module: { rules: [{ test: /\.html$/, use: [{ loader: 'html-loader', options: { minimize: true } }] }] } }

Other packages similar to html-loader

raw-loader

The raw-loader package is similar to html-loader in that it allows you to import files as a string. However, it does not specifically target HTML files and does not have HTML-specific features like minimizing.

handlebars-loader

The handlebars-loader is used for compiling Handlebars templates and includes them in the webpack bundle. It's similar to html-loader but is tailored for Handlebars template syntax.

pug-loader

The pug-loader package allows you to compile Pug templates and include them in your webpack bundle. It's similar to html-loader but is designed for the Pug templating engine (formerly known as Jade).

README

html-loader

Exports HTML as string. HTML is minimized when the compiler demands.

Getting Started

To begin, you'll need to install html-loader:

npm install --save-dev html-loader

or

yarn add -D html-loader

or

pnpm add -D html-loader

Then add the plugin to your webpack config. For example:

file.js

import html from "./file.html";

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
      },
    ],
  },
};

Options

• sources
• preprocessor
• postprocessor
• minimize
• esModule

sources

Type:

type sources =
  | boolean
  | {
      list?: Array<{
        tag?: string;
        attribute?: string;
        type?: string;
        filter?: (
          tag: string,
          attribute: string,
          attributes: string,
          resourcePath: string,
        ) => boolean;
      }>;
      urlFilter?: (
        attribute: string,
        value: string,
        resourcePath: string,
      ) => boolean;
      scriptingEnabled?: boolean;
    };

Default: true

By default every loadable attribute (for example - <img src="image.png">) is imported (const img = require('./image.png') or new URL("./image.png", import.meta.url)). You may need to specify loaders for images in your configuration (recommended asset modules).

Supported tags and attributes:

• the src attribute of the audio tag
• the src attribute of the embed tag
• the src attribute of the img tag
• the srcset attribute of the img tag
• the src attribute of the input tag
• the data attribute of the object tag
• the src attribute of the script tag
• the href attribute of the script tag
• the xlink:href attribute of the script tag
• the src attribute of the source tag
• the srcset attribute of the source tag
• the src attribute of the track tag
• the poster attribute of the video tag
• the src attribute of the video tag
• the xlink:href attribute of the image tag
• the href attribute of the image tag
• the xlink:href attribute of the use tag
• the href attribute of the use tag
• the href attribute of the link tag when the rel attribute contains stylesheet, icon, shortcut icon, mask-icon, apple-touch-icon, apple-touch-icon-precomposed, apple-touch-startup-image, manifest, prefetch, preload or when the itemprop attribute is image, logo, screenshot, thumbnailurl, contenturl, downloadurl, duringmedia, embedurl, installurl, layoutimage
• the imagesrcset attribute of the link tag when the rel attribute contains stylesheet, icon, shortcut icon, mask-icon, apple-touch-icon, apple-touch-icon-precomposed, apple-touch-startup-image, manifest, prefetch, preload
• the content attribute of the meta tag when the name attribute is msapplication-tileimage, msapplication-square70x70logo, msapplication-square150x150logo, msapplication-wide310x150logo, msapplication-square310x310logo, msapplication-config, twitter:image or when the property attribute is og:image, og:image:url, og:image:secure_url, og:audio, og:audio:secure_url, og:video, og:video:secure_url, vk:image or when the itemprop attribute is image, logo, screenshot, thumbnailurl, contenturl, downloadurl, duringmedia, embedurl, installurl, layoutimage
• the icon-uri value component in content attribute of the meta tag when the name attribute is msapplication-task

boolean

The true value enables the processing of all default elements and attributes, the false value disables the processing of all attributes.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          // Disables attributes processing
          sources: false,
        },
      },
    ],
  },
};

object

Allows you to specify which tags and attributes to process, filter them, filter urls and process sources starting with /.

For example:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            list: [
              // All default supported tags and attributes
              "...",
              {
                tag: "img",
                attribute: "data-src",
                type: "src",
              },
              {
                tag: "img",
                attribute: "data-srcset",
                type: "srcset",
              },
            ],
            urlFilter: (attribute, value, resourcePath) => {
              // The `attribute` argument contains a name of the HTML attribute.
              // The `value` argument contains a value of the HTML attribute.
              // The `resourcePath` argument contains a path to the loaded HTML file.

              if (/example\.pdf$/.test(value)) {
                return false;
              }

              return true;
            },
          },
        },
      },
    ],
  },
};

list

Type:

type list = Array<{
  tag?: string;
  attribute?: string;
  type?: string;
  filter?: (
    tag: string,
    attribute: string,
    attributes: string,
    resourcePath: string,
  ) => boolean;
}>;

Default: supported tags and attributes.

Allows to setup which tags and attributes to process and how, as well as the ability to filter some of them.

Using ... syntax allows you to extend default supported tags and attributes.

For example:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            list: [
              // All default supported tags and attributes
              "...",
              {
                tag: "img",
                attribute: "data-src",
                type: "src",
              },
              {
                tag: "img",
                attribute: "data-srcset",
                type: "srcset",
              },
              {
                // Tag name
                tag: "link",
                // Attribute name
                attribute: "href",
                // Type of processing, can be `src` or `scrset`
                type: "src",
                // Allow to filter some attributes
                filter: (tag, attribute, attributes, resourcePath) => {
                  // The `tag` argument contains a name of the HTML tag.
                  // The `attribute` argument contains a name of the HTML attribute.
                  // The `attributes` argument contains all attributes of the tag.
                  // The `resourcePath` argument contains a path to the loaded HTML file.

                  if (/my-html\.html$/.test(resourcePath)) {
                    return false;
                  }

                  if (!/stylesheet/i.test(attributes.rel)) {
                    return false;
                  }

                  if (
                    attributes.type &&
                    attributes.type.trim().toLowerCase() !== "text/css"
                  ) {
                    return false;
                  }

                  return true;
                },
              },
            ],
          },
        },
      },
    ],
  },
};

If the tag name is not specified it will process all the tags.

You can use your custom filter to specify html elements to be processed.

For example:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            list: [
              {
                // Attribute name
                attribute: "src",
                // Type of processing, can be `src` or `scrset`
                type: "src",
                // Allow to filter some attributes (optional)
                filter: (tag, attribute, attributes, resourcePath) => {
                  // The `tag` argument contains a name of the HTML tag.
                  // The `attribute` argument contains a name of the HTML attribute.
                  // The `attributes` argument contains all attributes of the tag.
                  // The `resourcePath` argument contains a path to the loaded HTML file.

                  // choose all HTML tags except img tag
                  return tag.toLowerCase() !== "img";
                },
              },
            ],
          },
        },
      },
    ],
  },
};

Filter can also be used to extend the supported elements and attributes.

For example, filter can help process meta tags that reference assets:

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            list: [
              {
                tag: "meta",
                attribute: "content",
                type: "src",
                filter: (tag, attribute, attributes, resourcePath) => {
                  if (
                    attributes.value === "og:image" ||
                    attributes.name === "twitter:image"
                  ) {
                    return true;
                  }

                  return false;
                },
              },
            ],
          },
        },
      },
    ],
  },
};

[!NOTE]

source with a tag option takes precedence over source without.

Filter can be used to disable default sources.

For example:

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            list: [
              "...",
              {
                tag: "img",
                attribute: "src",
                type: "src",
                filter: () => false,
              },
            ],
          },
        },
      },
    ],
  },
};

urlFilter

Type:

type urlFilter = (
  attribute: string,
  value: string,
  resourcePath: string,
) => boolean;

Default: undefined

Allow to filter urls. All filtered urls will not be resolved (left in the code as they were written). Non-requestable sources (for example <img src="javascript:void(0)">) are not handled by default.

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            urlFilter: (attribute, value, resourcePath) => {
              // The `attribute` argument contains a name of the HTML attribute.
              // The `value` argument contains a value of the HTML attribute.
              // The `resourcePath` argument contains a path to the loaded HTML file.

              if (/example\.pdf$/.test(value)) {
                return false;
              }

              return true;
            },
          },
        },
      },
    ],
  },
};

scriptingEnabled

Type:

type scriptingEnabled = boolean;

Default: true

By default, the parser in html-loader interprets content inside <noscript> tags as #text, so processing of content inside this tag will be ignored.

In order to enable processing inside <noscript> for content recognition by the parser as #AST, set this parameter to: false

Additional information: scriptingEnabled

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          sources: {
            // Enables processing inside the <noscript> tag
            scriptingEnabled: false,
          },
        },
      },
    ],
  },
};

preprocessor

Type:

type preprocessor = (content: string, loaderContext: LoaderContext) => string;

Default: undefined

Allows pre-processing of content before handling.

[!WARNING]

You should always return valid HTML

file.hbs

<div>
  <p>{{firstname}} {{lastname}}</p>
  <img src="image.png" alt="alt" />
<div>

function

You can set the preprocessor option as a function instance.

webpack.config.js

const Handlebars = require("handlebars");

module.exports = {
  module: {
    rules: [
      {
        test: /\.hbs$/i,
        loader: "html-loader",
        options: {
          preprocessor: (content, loaderContext) => {
            let result;

            try {
              result = Handlebars.compile(content)({
                firstname: "Value",
                lastname: "OtherValue",
              });
            } catch (error) {
              loaderContext.emitError(error);

              return content;
            }

            return result;
          },
        },
      },
    ],
  },
};

You can also set the preprocessor option as an asynchronous function instance.

For example:

webpack.config.js

const Handlebars = require("handlebars");

module.exports = {
  module: {
    rules: [
      {
        test: /\.hbs$/i,
        loader: "html-loader",
        options: {
          preprocessor: async (content, loaderContext) => {
            let result;

            try {
              result = await Handlebars.compile(content)({
                firstname: "Value",
                lastname: "OtherValue",
              });
            } catch (error) {
              await loaderContext.emitError(error);

              return content;
            }

            return result;
          },
        },
      },
    ],
  },
};

postprocessor

Type:

type postprocessor = (content: string, loaderContext: LoaderContext) => string;

Default: undefined

Allows post-processing of content after replacing all attributes (like src/srcset/etc).

file.html

<img src="image.png" />
<img src="<%= 'Hello ' + (1+1) %>" />
<img src="<%= require('./image.png') %>" />
<img src="<%= new URL('./image.png', import.meta.url) %>" />
<div><%= require('./gallery.html').default %></div>

function

You can set the postprocessor option as a function instance.

webpack.config.js

const Handlebars = require("handlebars");

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          postprocessor: (content, loaderContext) => {
            // When you environment supports template literals (using browserslist or options) we will generate code using them
            const isTemplateLiteralSupported = content[0] === "`";

            return content
              .replace(/<%=/g, isTemplateLiteralSupported ? `\${` : '" +')
              .replace(/%>/g, isTemplateLiteralSupported ? "}" : '+ "');
          },
        },
      },
    ],
  },
};

You can also set the postprocessor option as an asynchronous function instance.

For example:

webpack.config.js

const Handlebars = require("handlebars");

module.exports = {
  module: {
    rules: [
      {
        test: /\.hbs$/i,
        loader: "html-loader",
        options: {
          postprocessor: async (content, loaderContext) => {
            const value = await getValue();
            // When you environment supports template literals (using browserslist or options) we will generate code using them
            const isTemplateLiteralSupported = content[0] === "`";

            return content
              .replace(/<%=/g, isTemplateLiteralSupported ? `\${` : '" +')
              .replace(/%>/g, isTemplateLiteralSupported ? "}" : '+ "')
              .replace("my-value", value);
          },
        },
      },
    ],
  },
};

minimize

Type:

type minimize =
  | boolean
  | {
      caseSensitive?: boolean;
      collapseWhitespace?: boolean;
      conservativeCollapse?: boolean;
      keepClosingSlash?: boolean;
      minifyCSS?: boolean;
      minifyJS?: boolean;
      removeComments?: boolean;
      removeRedundantAttributes?: boolean;
      removeScriptTypeAttributes?: boolean;
      removeStyleLinkTypeAttributes?: boolean;
    };

Default: true in production mode, otherwise false

Tell html-loader to minimize HTML.

boolean

The enabled rules for minimizing by default are the following ones:

({
  caseSensitive: true,
  collapseWhitespace: true,
  conservativeCollapse: true,
  keepClosingSlash: true,
  minifyCSS: true,
  minifyJS: true,
  removeComments: true,
  removeRedundantAttributes: true,
  removeScriptTypeAttributes: true,
  removeStyleLinkTypeAttributes: true,
});

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          minimize: true,
        },
      },
    ],
  },
};

object

webpack.config.js

See html-minifier-terser's documentation for more information on the available options.

The default rules can be overridden using the following options in your webpack.conf.js

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          minimize: {
            removeComments: false,
            collapseWhitespace: false,
          },
        },
      },
    ],
  },
};

The default rules can be extended:

webpack.config.js

const { defaultMinimizerOptions } = require("html-loader");

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          minimize: {
            ...defaultMinimizerOptions,
            removeComments: false,
            collapseWhitespace: false,
          },
        },
      },
    ],
  },
};

esModule

Type:

type esModule = boolean;

Default: true

By default, html-loader generates JS modules that use the ES modules syntax. There are some cases in which using ES modules is beneficial, such as module concatenation and tree shaking.

You can enable a CommonJS modules syntax using:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {
          esModule: false,
        },
      },
    ],
  },
};

Examples

Disable url resolving using the <!-- webpackIgnore: true --> comment

With <!-- webpackIgnore: true --> comment, one can disable sources handling for next tag.

<!-- Disabled url handling for the src attribute -->
<!-- webpackIgnore: true -->
<img src="image.png" />

<!-- Disabled url handling for the src and srcset attributes -->
<!-- webpackIgnore: true -->
<img
  srcset="image.png 480w, image.png 768w"
  src="image.png"
  alt="Elva dressed as a fairy"
/>

<!-- Disabled url handling for the content attribute -->
<!-- webpackIgnore: true -->
<meta itemprop="image" content="./image.png" />

<!-- Disabled url handling for the href attribute -->
<!-- webpackIgnore: true -->
<link rel="icon" type="image/png" sizes="192x192" href="./image.png" />

roots

With resolve.roots one can specify a list of directories where requests of server-relative URLs (starting with '/') are resolved.

webpack.config.js

module.exports = {
  context: __dirname,
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: "html-loader",
        options: {},
      },
      {
        test: /\.jpg$/,
        type: "asset/resource",
      },
    ],
  },
  resolve: {
    roots: [path.resolve(__dirname, "fixtures")],
  },
};

file.html

<img src="/image.jpg" />

// => image.jpg in __dirname/fixtures will be resolved

CDN

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.jpg$/,
        type: "asset/resource",
      },
      {
        test: /\.png$/,
        type: "asset/inline",
      },
    ],
  },
  output: {
    publicPath: "http://cdn.example.com/[fullhash]/",
  },
};

file.html

<img src="image.jpg" data-src="image2x.png" />

index.js

require("html-loader!./file.html");

// => '<img src="http://cdn.example.com/49eba9f/a992ca.jpg" data-src="image2x.png">'

require('html-loader?{"sources":{"list":[{"tag":"img","attribute":"data-src","type":"src"}]}}!./file.html');

// => '<img src="image.jpg" data-src="data:image/png;base64,..." >'

require('html-loader?{"sources":{"list":[{"tag":"img","attribute":"src","type":"src"},{"tag":"img","attribute":"data-src","type":"src"}]}}!./file.html');

// => '<img src="http://cdn.example.com/49eba9f/a992ca.jpg" data-src="data:image/png;base64,..." >'

Process script and link tags

script.file.js

console.log(document);

style.file.css

a {
  color: red;
}

file.html

<!doctype html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>Title of the document</title>
    <link rel="stylesheet" type="text/css" href="./style.file.css" />
  </head>
  <body>
    Content of the document......
    <script src="./script.file.js"></script>
  </body>
</html>

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/,
        type: "asset/resource",
        generator: {
          filename: "[name][ext]",
        },
      },
      {
        test: /\.html$/i,
        use: ["html-loader"],
      },
      {
        test: /\.js$/i,
        exclude: /\.file.js$/i,
        loader: "babel-loader",
      },
      {
        test: /\.file.js$/i,
        type: "asset/resource",
      },
      {
        test: /\.css$/i,
        exclude: /\.file.css$/i,
        loader: "css-loader",
      },
      {
        test: /\.file.css$/i,
        type: "asset/resource",
      },
    ],
  },
};

Templating

You can use any template system. Below is an example for handlebars.

file.hbs

<div>
  <p>{{firstname}} {{lastname}}</p>
  <img src="image.png" alt="alt" />
<div>

webpack.config.js

const Handlebars = require("handlebars");

module.exports = {
  module: {
    rules: [
      {
        test: /\.hbs$/i,
        loader: "html-loader",
        options: {
          preprocessor: (content, loaderContext) => {
            let result;

            try {
              result = Handlebars.compile(content)({
                firstname: "Value",
                lastname: "OtherValue",
              });
            } catch (error) {
              loaderContext.emitError(error);

              return content;
            }

            return result;
          },
        },
      },
    ],
  },
};

PostHTML

You can use PostHTML without any additional loaders.

file.html

<img src="image.jpg" />

webpack.config.js

const posthtml = require("posthtml");
const posthtmlWebp = require("posthtml-webp");

module.exports = {
  module: {
    rules: [
      {
        test: /\.hbs$/i,
        loader: "html-loader",
        options: {
          preprocessor: (content, loaderContext) => {
            let result;

            try {
              result = posthtml().use(plugin).process(content, { sync: true });
            } catch (error) {
              loaderContext.emitError(error);

              return content;
            }

            return result.html;
          },
        },
      },
    ],
  },
};

Export into HTML files

A very common scenario is exporting the HTML into their own .html file, to serve them directly instead of injecting with javascript. This can be achieved with a combination of html-loader and asset modules.

The html-loader will parse the URLs, require the images and everything you expect. The extract loader will parse the javascript back into a proper html file, ensuring images are required and point to proper path, and the asset modules will write the .html file for you. Example:

webpack.config.js

module.exports = {
  output: {
    assetModuleFilename: "[name][ext]",
  },
  module: {
    rules: [
      {
        test: /\.html$/,
        type: "asset/resource",
        generator: {
          filename: "[name][ext]",
        },
      },
      {
        test: /\.html$/i,
        use: ["html-loader"],
      },
    ],
  },
};

Contributing

Please take a moment to read our contributing guidelines if you haven't yet done so.

CONTRIBUTING

License

MIT

Changelog

5.1.0 (2024-07-25)

Features

• added the postprocessor option (#518) (536a204)
• reduce runtime code (61f9a69)
• support absolute URLs and DataURI (#519) (cc34b06)
• using template literals in code when it supported (#520) (6fa80d5)