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

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

Name	Type	Default	Description
attributes	{Boolean|Object}	true	Enables/Disables attributes handling
preprocessor	{Function}	undefined	Allows pre-processing of content before handling
minimize	{Boolean|Object}	true in production mode, otherwise false	Tell html-loader to minimize HTML
esModule	{Boolean}	false	Use ES modules syntax

attributes

Type: Boolean|Object Default: true

By default every loadable attributes (for example - <img src="image.png">) is imported (const img = require('./image.png') or import img from "./image.png""). You may need to specify loaders for images in your configuration (recommended file-loader or url-loader).

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 href attribute of the link tag (only for stylesheets)
• the data attribute of the object tag
• the src 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

Boolean

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

webpack.config.js

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

Object

Allows you to specify which tags and attributes to process, filter them, filter urls and process sources starts with /. For example:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: 'html-loader',
        options: {
          attributes: {
            list: [
              {
                tag: 'img',
                attribute: 'src',
                type: 'src',
              },
              {
                tag: 'img',
                attribute: 'srcset',
                type: 'srcset',
              },
              {
                tag: 'img',
                attribute: 'data-src',
                type: 'src',
              },
              {
                tag: 'img',
                attribute: 'data-srcset',
                type: 'srcset',
              },
              {
                tag: 'link',
                attribute: 'href',
                type: 'src',
                filter: (tag, attribute, attributes) => {
                  if (!/stylesheet/i.test(attributes.rel)) {
                    return false;
                  }

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

                  return true;
                },
              },
              // More attributes
            ],
            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;
            },
            root: '.',
          },
        },
      },
    ],
  },
};

list

Type: Array Default: https://github.com/webpack-contrib/html-loader#attributes

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

For example:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        loader: 'html-loader',
        options: {
          attributes: {
            list: [
              {
                // Tag name
                tag: 'img',
                // Attribute name
                attribute: 'src',
                // Type of processing, can be `src` or `scrset`
                type: 'src',
              },
              {
                // Tag name
                tag: 'img',
                // Attribute name
                attribute: 'srcset',
                // Type of processing, can be `src` or `scrset`
                type: 'srcset',
              },
              {
                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: {
          attributes: {
            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';
                },
              },
            ],
          },
        },
      },
    ],
  },
};

urlFilter

Type: Function Default: undefined

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

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

root

Type: String Default: undefined

For urls that start with a /, the default behavior is to not translate them. If a root query parameter is set, however, it will be prepended to the url and then translated.

webpack.config.js

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

preprocessor

Type: Function Default: undefined

Allows pre-processing of content before handling.

⚠ 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;
          },
        },
      },
    ],
  },
};

minimize

Type: Boolean|Object 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:

• collapseWhitespace
• conservativeCollapse
• keepClosingSlash
• minifyCSS
• minifyJS
• removeAttributeQuotes
• removeComments
• removeScriptTypeAttributes
• removeStyleTypeAttributes
• useShortDoctype

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 rules can be disabled 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,
          },
        },
      },
    ],
  },
};

esModule

Type: Boolean Default: false

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

You can enable a ES module syntax using:

webpack.config.js

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

Examples

CDN

webpack.config.js

module.exports = {
  module: {
    rules: [
      { test: /\.jpg$/, loader: 'file-loader' },
      { test: /\.png$/, loader: 'url-loader' },
    ],
  },
  output: {
    publicPath: 'http://cdn.example.com/[hash]/',
  },
};

<!-- file.html -->
<img src="image.png" data-src="image2x.png" />

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

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

require('html-loader?attributes[]=img:data-src!./file.html');

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

require('html-loader?attributes[]=img:src&attributes[]=img:data-src!./file.html');

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

require('html-loader?-attributes!./file.html');

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

:warning: -attributes it is set attributes: false

'<img src=http://cdn.example.com/49eba9f/a9f92ca.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$/i,
        use: ['file-loader?name=[name].[ext]', 'extract-loader', 'html-loader'],
      },
      {
        test: /\.js$/i,
        exclude: /\.file.js$/i,
        loader: 'babel-loader',
      },
      {
        test: /\.file.js$/i,
        loader: 'file-loader',
      },
      {
        test: /\.css$/i,
        exclude: /\.file.css$/i,
        loader: 'css-loader',
      },
      {
        test: /\.file.css$/i,
        loader: 'file-loader',
      },
    ],
  },
};

'Root-relative' URLs

With the same configuration as above:

file.html

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

scripts.js

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

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

other-scripts.js

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

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

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: () => {
            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 3 loaders:

• file-loader
• extract-loader
• html-loader

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 file loader will write the .html file for you. Example:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.html$/i,
        use: ['file-loader?name=[name].[ext]', 'extract-loader', 'html-loader'],
      },
    ],
  },
};

Contributing

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

CONTRIBUTING

License

MIT

Changelog

1.1.0 (2020-04-02)

Features

• added support for an async functions to the preprocessor option (#272) (e59324b)
• allowed to handle an attribute without a tag (#273) (c0d6d5b)

Bug Fixes

• hash processing improved (#275) (74d2c60)