Elements and Rendering


A React Element is a component class, a set of parameters, and a group of children. When an element is rendered the parameters and used to initialize a new instance of the component.

React.create_element creates a new element. It takes either the component class, or a string (representing a built in tag such as div, or span), the parameters (properties) to be passed to the element, and optionally a block that will be evaluated to build the enclosed children elements

React.create_element("div", prop1: "foo", prop2: 12) { para { "hello" }; para { "goodby" } )
  # when rendered will generates <div prop1="foo" prop2="12"><p>hello</p><p>goodby</p></div>

You almost never need to directly call create_element, the DSL, Rails, and jQuery interfaces take care of this for you.

    # dsl - creates element and pushes it into the rendering buffer
    MyComponent(...params...) { ...optional children... }

    # dsl - component will NOT be placed in the rendering buffer
    MyComponent(...params...) { ... }.as_node

    # in a rails controller - renders component as the view
    render_component("MyComponent", ...params...)

    # in a rails view helper - renders component into the view (like a partial)
    react_component("MyComponent", ...)

    # from jQuery (Note Element is the Opal jQuery wrapper, not be confused with React::Element)
    Element['#container'].render { MyComponent(...params...) { ...optional children... } }  



Verifies object is a valid react element. Note that React::Element wraps the React.js native class, React.is_valid_element? returns true for both classes unlike object.is_a? React::Element


React.render(element, container) { puts "element rendered" }

Render an element into the DOM in the supplied container and return a reference to the component.

The container can either be a DOM node or a jQuery selector (i.e. Element['#container']) in which case the first element is the container.

If the element was previously rendered into container, this will perform an update on it and only mutate the DOM as necessary to reflect the latest React component.

If the optional block is provided, it will be executed after the component is rendered or updated.


React.render() controls the contents of the container node you pass in. Any existing DOM elements inside are replaced when first called. Later calls use React’s DOM diffing algorithm for efficient updates.

React.render() does not modify the container node (only modifies the children of the container). In the future, it may be possible to insert a component to an existing DOM node without overwriting the existing children.



Remove a mounted React component from the DOM and clean up its event handlers and state. If no component was mounted in the container, calling this function does nothing. Returns true if a component was unmounted and false if there was no component to unmount.



Render an element to its initial HTML. This is should only be used on the server for prerendering content. React will return a string containing the HTML. You can use this method to generate HTML on the server and send the markup down on the initial request for faster page loads and to allow search engines to crawl your pages for SEO purposes.

If you call React.render on a node that already has this server-rendered markup, React will preserve it and only attach event handlers, allowing you to have a very performant first-load experience.

If you are using rails, then the prerendering functions are automatically performed. Otherwise you can use render_to_string to build your own prerendering system.



Similar to render_to_string, except this doesn't create extra DOM attributes such as data-react-id, that React uses internally. This is useful if you want to use React as a simple static page generator, as stripping away the extra attributes can save lots of bytes.


Hyperloop Components are ruby classes that either subclass Hyperloop::Component, or mixin Hyperloop::Component::Mixin. Both mechanisms have the same effect.

Instances of React Components are created internally by React when rendering. The instances exist through subsequent renders, and although coupled to React, act like normal ruby instances. The only way to get a valid reference to a React Component instance outside of React is by storing the return value of React.render. Inside other Components, you may use refs to achieve the same result.