The Lit filter makes it easier to build LitElement web components. Here’s an example of a component from Lit’s documentation, rewritten in Ruby2JS (and you can inspect the compiled output to see nearly identical code.)

class SimpleGreeting < LitElement
  self.styles = <<~CSS
    p { color: blue }

  custom_element "simple-greeting"

  def initialize
    @name = "Somebody"

  def render
      <p>Hello, #{name}!</p>

List of Transformations

When a class definition is encountered that derives from LitElement, the following transformations are applied:

  • an import statement for LitElement will be generated if the esm filter is also applied.

  • instance variables (e.g., @x) are not mapped to properties prefixed with either an underscore (_) or a hash (#).

  • References to instance variables will cause entries to be added to the static properties property if not already present, and simple type inferencing will be used to determine the type. (To bypass this for truly internal state, use a prefixed ivar name like @_x.)

  • @styles assignments, self.styles assignments and self.styles methods that return a string will have that string mapped to a css literal string. These are three alternate syntaxes to specifying static styles.

  • render and other methods that return a string will have that string mapped to a html literal string if that string starts with a less than sign. This also applies, recursively, to all interpolated values within that string. (For a method where you don’t want the html literal used, just return a string variable or some such statement instead.)

  • Methods referenced within HTML literals are not automatically bound, but will be automatically prefixed with this..

  • LitElement inheritance will also automatically prefix inherited properties and methods with this., and will autobind inherited methods when referenced without any parameters or parenthesis.
    • methods: performUpdate,requestUpdate
    • properties: hasUpdated, renderRoot, shadowRoot, updateComplete
  • customElement (or custom_element) calls are converted to customElements.define calls.

  • query, queryAll, and queryAsync calls are converted to corresponding this.renderRoot.querySelector calls.

  • If super is not called by the initialize function, a call to super will be added.