A robust command-line tool for converting Polymer 3 components to Lit (LitElement).

• ✅ Automatic conversion of Polymer 3 components to Lit
• ✅ Template conversion from Polymer's HTML templates to Lit's template literals
• ✅ Property binding conversion including one-way ([[]]) and two-way ({{}}) bindings
• ✅ Event handler conversion from on-* attributes to @ event listeners
• ✅ Style handling with support for custom styles and style includes
• ✅ DOM manipulation conversion (this.$ to this.renderRoot.querySelector)
• ✅ Batch processing support for entire directories
• ✅ Configurable output with Lit 1.x or 2.x support
• ✅ Error handling with graceful fallbacks
• ✅ Debug and verbose modes for troubleshooting

cd frontend
npm install
npx tsc

Convert a single Polymer component:

node frontend/convert.js my-component.js -out

Convert all components in a directory:

node frontend/convert.js ./src -out

// Polymer
static get template() {
  return html`<div>[[property]]</div>`;
}

// Lit
render() {
  return html`<div>${this.property}</div>`;
}

• Property bindings: [[prop]] → ${this.prop}
• Two-way bindings: {{prop}} → ${this.prop} + event handler
• Event handlers: on-click="handler" → @click=${this.handler}
• DOM access: this.$.id → this.renderRoot.querySelector("#id")

The frontend tool is in the frontend folder.

cd frontend
npm install
npx tsc

Convert a single file with output suffix:

node convert.js my-component.js -out

This will convert my-component.js into a Lit element and save it as my-component.js.out.js

Convert with verbose output:

node convert.js my-component.js -out -v

Get help:

node convert.js --help

The Java tool is in the java folder

To test this tool, do the setup dance once

cd java
mvn package

Then run it and give it a PolymerTemplate Java file

mvn exec:exec -Dfile=/my/project/src/main/java/my/package/MyTemplate.java