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0.1.0 • Public • Published


Node module to create a bundle import file from ARC or any Polymer powered components. It also generates React wrapper definition for the components using wc-reactor module.

What does it do?

Let's start what it doesn't do. It doesn't creates a new React components based on web components definition. After creating React wrapper you still have to use import.html file with bundled web components definitions.

This library generates a bundle file of web components. It can be used to optimize number of imports declaration in the web application. Under the hood it uses polymer-build library so it basically do the same thing with bundling the components.

Another thing it does is generating a React wrapper for the web components so it can be used in React application. It creates exactly the same interface as web components uses. It handles all custom events, property change events and data binding (in a React way).


const builder = require('arc-components-builder');
  // Any web component, it can contain version declaration
  webComponents: [
  // Any ARC component, it also can contain version declaration
  arcComponents: [
  // print debug output
  verbose: true,
  // Creates React wrapper
  react: true,
  // Create React interface for the following components only.
  reactComponents: ['url-input-editor']
.then(() => console.log('Build complete <3'));

The result of building the components is located in ./build directory. It's structure is:

| build/
  | - bower-components/
      | - ...
  | - UrlInputEditor
      | - UrlInputEditor.js
      | - index.js
  | - import.html

Most important files are import.html and UrlInputEditor/UrlInputEditor.js. The import file contains a bundle of web components defined in webComponents and arcComponents configuration directive as well as all it's dependencies. This is single file build of included web components.

The React component file contains autogenerated interface to communicate with web components in a React application. Check names mapping section below to understand how to map event names to React functions.

The bower_components directory contains all used web components definition. It can be useful if the components that are bundled in import.html file contains a reference to a resource in bower_components directory that couldn't been processed by polymer-build (like dynamically loaded JS library from component's directory). You may want to copy components directory to your web server. In most cases it won't be used at all.

Names mapping in React component

React wrapper contains interface to manipulate web component's properties, handle custom events (including properties change events) and to call public API functions.

Properties mapping

Web components property names are the same as React's props. So you can use generated component like this:

render() {
  return (
    <PaperCombobox label="My label" value={this.props.value}/>

When the PaperCombobox component is mounted then the label and value properties are propagated to the underlying web component. The same is happening each time when React's state change:

 * Updates list of suggestion in the PaperCombobox web component
updateSuggestions() {
    source: ['One', 'Two', 'Three']
render() {
  return (
    <PaperCombobox label="My label" source={this.state.source}/>

Updating the sate value will update corresponding web component's property.

Polymer's data binding

Polymer powered web components uses Polymer's data binding for properties. This can be easily done in react by using on + propertyName + Changed function set to a property.

Assuming that the PaperCombobox web component has value property that notify value change (sends non-bubbling custom event when value changes). You can handle it in React application using functions:

_onValueChanged(newValue, e) {
render() {
  return (
    <PaperCombobox label="My label" source={this.state.source} onValueChanged={this._onValueChanged}/>

New value and original event is always passed to data binding change function calls. You can use event to access additional data like information about the target or path. Note, that target may not be the web component but an element inside it.

Note: Only public properties are handled by the wrapper. It doesn't work with protected properties (property name starts with _).

Methods mapping

Methods are mapped 1:1 from the web component. Only public methods are available to wrapper. Web component's lifecycle methods are also unavailable.

Let's assume that the PaperCombobox element has a selectNext method in it's public API:

selectNextDropdownItem() {
render() {
  return (
    <PaperCombobox ref={(element) => {this._refElement = element;}}/>

Events mapping

Custom events names are translated to camel case function call as: on + UppercaseCamelCaseEventName.

Custom event's detail object and the event itself is passed as an argument to the function call.

Assuming that the paper-combobox web components dispatches next-selected event. It can be handled by setting onNextSelected property on the components that is a handler for event.

_comboNextSelected(detail, e) {
  console.log(e.target, e.path);
  console.log('Next element selected', detail);
  // detail === e.detail
render() {
  return (
    <PaperCombobox onNextSelected={this._comboNextSelected}/>

The script above handles the next-selected event and passes the detail of the event to the function.

More examples

Checkout our example build usage project to see how to use generated module in React application: https://github.com/advanced-rest-client/arc-components-builder-example


All options are defined in lib/project-options.js.

arcComponents {Array<String>}

A list of ARC web components to be used. It should be a list of names of the components only, without advanced-rest-client/ prefix as it will be added by the program.

You can control version of the component by adding version number for the components as in npm or bower.

Example: ['paper-autocomplete#1.0.0', 'raml-request-panel#^1.1.0']

webComponents {Array<String>}

The same as arcComponents but it must be full bower definition of the component dependency.

Example: ['PolymerElements/paper-input', 'PolymerElements/paper-icon-button#1.0.0']

style {String}

Path to custom-style module with theme definition for the ARC / web components.

dev {Boolean}

If set it will not create a bundle file but only an import file with references to bower_components directory where the source code of the elements is downloaded. It can be helpful for dubugging when you want to debug specific element without braking current dev setup.

The build directory contains the import file and bower_components. Both should be copied to server and put into the same location.

react {Boolean}

Specify to generate React components definition from the elements. Generated source file contains classes definitions for each component with access points to all public APIs of the element (properties, functions and custom events).

reactComponents {Array<String>}

List of web components names to be exposed to generated React component so it can be included in React application.

Defining this option is optional. By default all listed components in arcComponents and webComponents properties are exposed to React application.

To reduce size of generated code it is a good idea to declare number of components that your application is actually using.

Provide list of components names only, without any repository path or version information.

For example ['raml-request-panel', 'paper-input']

bundleReactComponents {Boolean}

By default it creates a separate React file for each web component that is to be wrapped in React code. When this option is set then it bundles all React components into a single file and exports each React component in this file.

This can be set only if react option is set.

dest {String}

The destination where the build files are put. Absolute or relative path.

By default it puts the files into build directory of the working dir.

logger {Object}

Instance of any logger library that has log(), info(), warn() and error() functions. If not provided a console's output will be used.

verbose {Boolean}

If set then it prints verbose messages.

Double events problem

Sometimes Polymer web components sends an event that has the same name as data binding event. In this case you will notice two handler function calls with different set of arguments.

Polymer powered web component can contain a property declaration with notify set to true. It is used by the data binding system to update property value on a parent element / application. Those change events does not bubble. They can be only handled when setting an event listener on the element. That's is why sometimes authors prefer to send additional event with the same name that bubbles through the DOM. Consider the following example:

// Polymer element (v1)
  is: 'paper-combobox',
  properties: {
    value: {
      type: String,
      notify: true,
      observer: '_valueChanged'
  _valueChanged: function(value) {
    this.fire('value-changed', {
      value: value

This components sends two value-changed events when the value property have changed. Because of the name collision the React wrapper automatically calls onValueChanged prop function as a data binding automated function and then it also listens for the value-changed event and calls the same onValueChanged function.

Automated change handler functions have a value of changed property as the first argument. Regulars event handlers have event's detail object as a first argument. Therefore you may end up handling the same event twice but with different argument.


  1. Fork it
  2. Create your feature branch: git checkout -b my-new-feature
  3. Commit your changes: git commit -am 'Add some feature'
  4. Push to the branch: git push origin my-new-feature
  5. Submit a pull request <3

Supported Node.js Versions

arc-components-builder officially supports the latest current & active LTS versions of Node.js. It may be working with previous versions but it is not intentional.




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