babel-plugin-template-html-minifier

Minify HTML in tagged template strings using html-minifier-terser.

Install

npm install --save-dev babel-plugin-template-html-minifier

Usage

In .babelrc:

{
  "plugins": [
    ["template-html-minifier", {
      "modules": {
        "choo/html": [null],
        "hyperhtml": [{"name": "bind", "type": "factory"}],
        "hyperhtml-element": [{"name": null, "member": "html"}]
      },
      "htmlMinifier": {
        "collapseWhitespace": true
      }
    }]
  ]
}

Example for lit-html and lit-element:

{
  "plugins": [
    ["template-html-minifier", {
      "modules": {
        "lit-html": ["html"],
        "lit-element": [
          "html",
          {"name": "css", "encapsulation": "style"}
        ],
      },
      "strictCSS": true,
      "htmlMinifier": {
        "collapseWhitespace": true,
        "conservativeCollapse": true,
        "removeComments": true,
        "caseSensitive": true,
        "minifyCSS": true
      },
    }]
  ]
}

Options

htmlMinifier

The value of this property is passed unmodified to html-minifier-terser. See the html-minifier-terser docs.

Note for usage with lit-html and lit-element:

• To preserve case sensitiveness of property binding "caseSensitive": true must be added.

• collapseBooleanAttributes should not be used when working with lit-html or other templating systems which give special meaning to non-static boolean attributes. Enabling collapseBooleanAttributes will cause this plugin to throw an exception:

  html`<input readonly="${readonly}">`;

  This exception is for two reasons. First because it means the chosen options have caused html-minifier-terser to change the meaning of the HTML template. Second because it deletes the point where ${readonly} goes into the final output.

• removeComments will cause the following template to throw an exception:

  html`<!-- <input value="${value}"> -->`;

  This exception is because ${value} inside an HTML template gets deleted. It should be noted that an HTML template does not prevent code within ${} from running. This means that in the following template getValue() is still executed when processing the html template:

  html`<!-- <input value="${getValue()}"> -->`;

  It is recommended to use binding-positions from eslint-plugin-lit to catch this error. This babel transformation can only determine that a template is broken, the eslint plugin will tell you which binding is invalid.

strictCSS

Whether CSS should only be minified when it is valid CSS. This is necessary when using css templates which allow multiple strings of invalid CSS together to make a valid stylesheet. This is the case for example with lit-element:

const unit = css`px`;
const widthXL = 400;
const styleSheet = css`
  @media (${widthXL}px) {
    .foo {
      font-size: 16${unit};
    }
  }
`;

Minification happens per template literal, it is only able to see the unconcatenated css literals and minify those. It will try to do the right thing, but it cannot handle every scenario. If you are using lit-element, and write these types of templates, you need to set strictCSS to true.

modules

A list of module names or import paths where tags are imported from. The values in the arrays refers to the export names, not the import names. null refers to the default export.

failOnError

Determines whether an error should be thrown when minification failed. defaults to true.

Minification can fail when using invalid syntax or comments within bindings. Especially when using css with bindings minification can fail. When failOnError is true, this plugin throws an error and your build will stop from proceeding. When it is false the minification is canceled and the template is left unminified.

logOnError

Determines whether failure to minify a template should be logged in case of an error. Defaults to true. This setting only takes effect when failOnError is false.

import choo from 'choo/html';
import * as lit from 'lit-html';
import {html as litHtml, css} from 'lit-element';
import HyperHTMLElement from 'hyperhtml-element';
import html from 'some-module';
import {bind} from 'hyperhtml';

choo`
  <div class="hello">
    Hello World
  </div>
`;

lit.html`
  <div class="hello">
    Hello World
  </div>
`;

litHtml`
  <div class="hello">
    Hello World
  </div>
`;

css`
  .sel {
    background: red;
  }
`;

class MyHyperHTMLElement extends HyperHTMLElement {
  created() {
    this.render();
  }

  render() {
    this.html`
      <div>
        Hello World
      </div>
    `;
  }
}

bind(document.body)`
  <div>
    Hello World
  </div>
`;

html`
  This
  is
  not
  processed
`;

Using the .babelrc shown in usage produces the following output:

import choo from 'choo/html';
import * as lit from 'lit-html';
import {html as litHtml, css} from 'lit-element';
import HyperHTMLElement from 'hyperhtml-element';
import html from 'some-module';
import {bind} from 'hyperhtml';

choo`<div class="hello"> Hello World </div>`;

lit.html`<div class="hello"> Hello World </div>`;

litHtml`<div class="hello"> Hello World </div>`;

css`.sel{background:red}`;

class MyHyperHTMLElement extends HyperHTMLElement {
  created() {
    this.render();
  }

  render() {
    this.html`<div> Hello World </div>`;
  }
}

bind(document.body)`<div> Hello World </div>`;

html`
  This
  is
  not
  processed
`;

• choo is processed because of "choo/html": [null] specifies that the default export should be processed.
• lit.html is processed because "lit-html": ["html"].
• litHtml is processed because "lit-element": ["html"].
• css is processed because "lit-element": [{"name": "css", "encapsulation": "style"}]. The encapsulation argument ensures that html-minifier-terser understands that the template contains CSS, without it the template would be processed as HTML.
• this.html in MyHyperHTMLElement is processed because "hyperhtml-element": [{"name": null, "member": "html"}] specifies that the html member of classes which extend the default export should be processed.
• bind is processed because of "hyperhtml": [{"name": "bind", "type": "factory"}], the type factory specifies the bind returns a function which processes the tagged templates.
• html is not processed because it was exported from an unlisted module.

All matching is done based on the exported name, not the local/imported name.

Running tests

Tests are provided by xo and ava.

npm install
npm test

Attribution

This module was originally created by goto-bus-stop.

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