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The unknown-prop warning will fire if you attempt to render a DOM element with a prop that is not recognized by React as a legal DOM attribute/property. You should ensure that your DOM elements do not have spurious props floating around.

There are a couple of likely reasons this warning could be appearing:

  1. Are you using {...this.props} or cloneElement(element, this.props)? Your component is transferring its own props directly to a child element (eg. When transferring props to a child component, you should ensure that you are not accidentally forwarding props that were intended to be interpreted by the parent component.

  2. You are using a non-standard DOM attribute on a native DOM node, perhaps to represent custom data. If you are trying to attach custom data to a standard DOM element, consider using a custom data attribute (

  3. React does not yet reco

jimfb / wrapper.js
Last active November 6, 2018 04:41
class MyWrapper {
return React.Children.only(this.props.children);
class MyLibraryComponent {
render() {
return <div><span><whatever><MyWrapper ref=...>{this.props.statelessComponentThatIWantToReference}</MyWrapper></whatever></span></div>;
jimfb / gist:fb2a04fe3fa4637d7d62
Created December 30, 2015 05:37
Special React Props

Most props on a JSX element are passed on to the component, however, there are two special props (ref and key) which are used by React, and are thus not forwarded to the component.

For instance, attempting to access this.props.key from a component (eg. the render function) is not defined. If you need to access the same value within the child component, you should pass it as a different prop (ex: <ListItemWrapper key={} id={} />) While this may seem redundant, it's important to separate app logic from reconciling hints.

Suppose a parent renders <ChildComponent callback={(value)=>setState(value)} />. Suppose the parent re-renders. The pointer values of the callback prop will be different (ie. not triple-equals-equal) but the callback prop's value is conceptually the same for all intents and purposes. This is a "new value" despite being the "same value". You run into the same problem when the parent creates an object <ChildComponent data={{foo: 'bar', bar: 'noise'}} /> (pointers differ, despite it being the "same" object from a value-type perspective).

You also run into the reverse problem due to mutability. Suppose I say:

var value = {foo: 'bar', bar: 'noise'};
ReactDOM.render(<ChildComponent data={value} />, ...); = 'drinks';
ReactDOM.render(<ChildComponent data={value} />, ...);
jimfb /
Last active July 13, 2019 06:35
addComponentAsRefTo Invariant Violation

You are probably here because you got the following error messages:

addComponentAsRefTo(...): Only a ReactOwner can have refs. You might be adding a ref to a component that was not created inside a component's render method, or you have multiple copies of React loaded.

This usually means one of two things:

  • You are trying to add a ref to an element that is being created outside of a component's render() function.
  • You have multiple (conflicting) copies of React loaded (eg. due to a miss-configured NPM dependency)

Invalid Refs

jimfb / gist:0eb6e61f300a8c1b2ce7
Last active January 22, 2022 01:52
Parent vs. Owner Context

If you've reached this page, it's probably because your "parent-based and owner-based contexts differ".

As we've been iterating on React's "context" feature, we've discovered that the parent-based relationship is more useful than the owner-based relationship, so we're migrating to use a parent-based hierarchy.

In short, the owner of a component is whomever creates the component, while the parent of a component is whomever would be the containing ancestor in the DOM hierarchy. To learn more about the owner relationship, see the docs here:

In many cases, the owner and the parent are the same node, in which case, no further action is necessary.