We think the validations will be simpler with an <Image /> component, something like:

  optionalUnion: React.PropTypes.oneOfType([
      React.PropTypes.instanceOf(Image),
      React.PropTypes.instanceOf(Svg),
      React.PropTypes.instanceOf(Icon)
    ]),

But yeah, that will have to wait...

To check if a ReactElement has a particular type, check its .type property:

var img = <Image />;
img.type === Image  // true

There's no built-in PropTypes validator to check for an element with a particular type.

You need to be really careful when checking against the type field of a ReactElement. When done the naive way, it prevents you from writing abstractions.

For example, if you only accept a prop img that satisfies img.type === Image, then it only accepts a literal <Image ...> component. But it won't accept a higher level component like <ProfilePicture> that eventually renders an <Image> component.

@spicyj @vjeux I'm having difficulty getting a ReactElement to return its type the way you specified... my reproduction produced the following:

var img = <Image />
img.type === Image // false
console.log(img.type)

outputs...

function (props) {
      // This constructor is overridden by mocks. The argument is used
      // by mocks to assert on what gets mounted. This will later be used
      // by the stand-alone class implementation.
}

which comes from ReactClass.js. Would love any feedback to clarify my understanding of how to use the type field of ReactElements!