Why doesn't React cache html elements of child components?

Question

Hiello!

I'm wondering whats wrong in the React example bellow or if React works differently than I thought?

I'm looking for a way to reuse the underlying html element for a child react component, when the parents are two different components.

In the example bellow, I would like the inside the Circle component to have the same element after renderC1 and renderC2 is called. For instance so that I could apply a transition css property to animate the color switch, like they would if I e.g. just changed the style directly on the element.

When I render the bellow, React always seems to generate different HTML elements, ref, key or id on the DIV (in the render function of Circle) doesn't help much.

So my questions: is it possible to get React to just reuse the DIV that gets rendered via C1 when C2 is rendered? I thought this was how React should work, optimizing the underlying HTML elements?

Something like:

var C1 = React.createClass({
  render: function () {
    return (
        <Circle background="deeppink" onClick={renderC2}/>
     );
  }
});

function renderC1 () {
  React.render(
    <C1 />, 
    document.getElementById('mount-point'));
}

var C2 = React.createClass({
  render: function () {
    return (
        <Circle background="salmon" onClick={renderC1}/>
     );
  }
});

function renderC2 () {
      React.render(
    <C2 />, 
    document.getElementById('mount-point'));
}

var Circle = React.createClass({
  styler: {
    width: "100px",
    height: "100px",
    mozBorderRadius: "50%",
    webkitBorderRadius: "50%",
    borderRadius: "50%",
    background: 'hotpink'
  },

  componentWillMount: function() {
    if (this.props && this.props.background &&
       this.props.background !== this.styler.background) {
         this.styler.background = this.props.background;
    }
  },

  render: function() {
    return (
      {/* tried adding key, ref and id, but does not reuse element */}
      <div onClick={this.props.onClick} style={this.styler}></div>
    );
  }
});

renderC1();

There isn't reuse of elements. You can't have the same DOM element be a child of multiple parents. — WiredPrairie, Mar 29 '15 at 12:20
You might have a look at http://stackoverflow.com/questions/21109361/why-is-reacts-concept-of-virtual-dom-said-to-be-more-performant-than-dirty-mode and https://facebook.github.io/react/docs/working-with-the-browser.html — WiredPrairie, Mar 29 '15 at 12:23

Kyeotic · Accepted Answer · 2015-12-22T20:54:38.243

This is impossible. The DOM does not allow one element to be in two places at once. Attempting to put a DOM element in a new location will automatically remove it from the old location.

You can see that here. (or more visually, here)

var parent1 = document.createElement('div'),
    parent2 = document.createElement('div'),
    child = document.createElement('div'),
    results = document.createElement('span');

  document.body.appendChild(results);
        
  parent1.appendChild(child);
  results.textContent += child.parentNode === parent1; //true
  parent2.appendChild(child);
  results.textContent += ', ' + (child.parentNode === parent1); //false

Why doesn't React cache html elements of child components?

1 Answers1