A Stateful Component

A Stateful Component

This example focuses on managing state, and making use of React component lifecycle methods.

While it is possible to use this.state to reference state and this.setState to update state within React components expressed in Ruby syntax, the more natural way to express state in Ruby classes is with instance variables (for example, @seconds).

class Timer < React
  def initialize
    @seconds = 0

  def tick()
    @seconds += 1

  def componentDidMount()
    self.interval = setInterval(tick, 1_000)

  def componentWillUnmount()

  def render
    React.createElement 'div', nil, 'Seconds: ', @seconds

  React.createElement(Timer, nil),



Statement by statement:

  • For convenience, this filter will convert classes that inherit simply from React as well as React::Component to React components.

  • JavaScript constructor becomes Ruby’s initialize. Defining a props argument and calling super is optional, and will be done for you automatically if necessary (in this example, props is not needed). Defining initial values is done by instance variable assignment rather than explicitly creating a this.state object.

  • The tick method updates state via an assignment statement rather than by calling the setState method.

  • The componentDidMount lifecycle method will cause the tick method to be called every 1,000 milliseconds. Notes:
    • The tick method can be passed directly without the need for an anonymous function.
    • self.instance is a property on the instance that is not a part of React’s state for the object.
  • The componentWillUnmount lifecycle method will cancel the timer.

  • The render method outputs the number of seconds within an HTML div element. With React.js, the use of JSX is optional and you can directly code calls to React.createElement, and this works in Ruby2JS too.

  • The ReactDOM.render method also accepts calls to React.createElement.

Next: A Todo Application