Web Components Codemods

Codemods for Web Components.
Breaking changes? Don't panic :)

Table of contents

• Usage
  • Using the included CLI
  • Using jscodeshift
• Available codemods
  • Replace attrs
  • Replace block scope by IIFE
  • Rename tag
  • LitElement to Lit imports
• Acknowledgments

Usage

The available codemods can be run in two ways: by using the included CLI or running the transform scripts directly with jscodeshift.

Using the included CLI

Install this package globally:

npm i -g web-components-codemods

Run the command in the directory you want to run a transform (the directory can be changed later):

kodemod

The command will prompt you for the transform to run and all of its options.

Alternatively, you can run a specific transform by running kodemod <transform>.

Example:

kodemod replace-attrs

Available transform commands (same as transform scripts):

• replace-attrs
• block-scope-to-iife
• rename-tag
• lit-element-to-lit-imports

Using jscodeshift

Install jscodeshift globally:

npm i -g jscodeshift

Clone or download this repository:

npx degit kcmr/web-components-codemods

Run jscodeshift passing the transform script with the -t option:

jscodeshift target-dir/*.js -t web-components-codemods/<transform-script>.js

Available codemods

Replace attrs

Replaces attributes in the specified tag inside a template literal tagged html (LitElement or lit-html).

Script: transforms/replace-attrs.js

Options

Name	Default	Type	Description
--tag	undefined	String	Tag name where the attributes will be replaced
--attrs	undefined	String	Stringified object with {'old-attr': 'new-attr'} pairs
--tabWidth	4	Number	Number of spaces used per tab
--useTabs	false	Boolean	Use tabs instead of spaces

Example input:

class MyComponent extends LitElement {
  render() {
    return html`
      <some-component
        attr-one="value"
        attr-two="${expression}"
        .someProp="${expression}"
      >
      </some-component>
    `;
  }
}

Command with options:

jscodeshift input.js -t replace-attrs.js --tag=some-component --attrs='{"attr-one": "foo", ".someProp": ".newProp"}'

Output:

class MyComponent extends LitElement {
  render() {
    return html`
      <some-component
-        attr-one="value"
+        foo="value"
        attr-two="${expression}"
-        .someProp="${expression}"
+        .newProp="${expression}"
      >
      </some-component>
    `;
  }
}

Replace block scope by IIFE

Replaces brackets used as scope in a file by an IIFE.

Script: transforms/block-scope-to-iife.js

Options: no options.

Example input:

{
  const { Element } = Polymer;
}

Command with options:

jscodeshift input.js -t block-scope-to-iife.js

Output:

-{
+(function() {
  const { Element } = Polymer;
+})();
-}

Rename tag

Renames a tag name inside template literals and strings.

Script: transforms/rename-tag.js

Options

Name	Default	Type	Description
--oldTag	undefined	String	Tag name to replace
--newTag	undefined	String	New tag name
--tabWidth	2	Number	Number of spaces used per tab
--useTabs	false	Boolean	Use tabs instead of spaces

Example input:

const tpl = `
  <some-tag>
    <some-tag-two></some-tag-two>
  </some-tag>
`;
customElements.define('some-tag', SomeTag);

Command with options:

jscodeshift input.js -t rename-tag.js --oldTag=some-tag --newTag=new-tag

Output:

const tpl = `
-  <some-tag>
+  <new-tag>
    <some-tag-two></some-tag-two>
-  </some-tag>
+  </new-tag>
`;
-customElements.define('some-tag', SomeTag);
+customElements.define('new-tag', SomeTag);

LitElement to Lit imports

Updates the imports from lit-element to lit according to the upgrade guide of Lit 2.0

Script: transforms/lit-element-to-lit-imports.js

Options:

Name	Default	Type	Description
--quote	single	String	Type of quote (single or double)

Example input:

import { css } from 'lit-element';
import { LitElement, html, property as foo, customElement } from 'lit-element';
import { repeat } from 'lit-html/directives/repeat.js';
import { ifDefined } from 'lit-html/directives/if-defined';

Command with options:

jscodeshift input.js -t lit-element-to-lit-imports.js

Output:

-import { css } from 'lit-element';
+import { css } from 'lit';
-import { LitElement, html, property as foo, customElement } from 'lit-element';
+import { LitElement, html } from 'lit';
+import { property as foo, customElement } from 'lit/decorators.js';
-import { repeat } from 'lit-html/directives/repeat.js';
+import { repeat } from 'lit/directives/repeat.js';
-import { ifDefined } from 'lit-html/directives/if-defined';
+import { ifDefined } from 'lit/directives/if-defined';

Acknowledgments

Inspiration

• Fearless refactors con AST - Speaker Deck
• React Codemod

Resources

• Write Code to Rewrite Your Code: jscodeshift
• jscodeshift API and demos

License

This project is licensed under the MIT License.