Can a React prop type be defined recursively?

Question

Suppose we're defining a React class that will display a tree.

React.createClass({
    propTypes: {
        tree: treeType
    },
    render: function () {
        // ...
    }
});

Here's a definition of treeType that obviously doesn't work but hopefully illustrates what I'm trying to express.

var treeType = React.PropTypes.shape({
    value: React.PropTypes.string,
    children: React.PropTypes.arrayOf(treeType)
})

Is there a way to let the type refer to itself lazily so this can work?

Answer 1

A React prop type is just a function, so it can be referenced lazily like this:

function lazyFunction(f) {
    return function () {
        return f.apply(this, arguments);
    };
}

var lazyTreeType = lazyFunction(function () { 
    return treeType;
});

var treeType = React.PropTypes.shape({
    value: React.PropTypes.string.isRequired,
    children: React.PropTypes.arrayOf(lazyTreeType)
})

The rest of the code for a complete working example (also available as a jsfiddle):

function hasChildren(tree) {
    return !!(tree.children && tree.children.length);
}

var Tree = React.createClass({
    propTypes: {
        tree: treeType
    },
    render: function () {
        return this.renderForest([this.props.tree], '');
    },
    renderTree: function (tree, key) {
        return <li className="tree" key={key}>
            <div title={key}>{tree.value}</div>
            {hasChildren(tree) &&
                this.renderForest(tree.children, key)}
        </li>;
    },
    renderForest: function (trees, key) {
        return <ol>{trees.map(function (tree) {
            return this.renderTree(tree, key + ' | ' + tree.value);
        }.bind(this))}</ol>;
    }
});

var treeOfLife = { value: "Life", children: [
    {value: "Animal", children: [
        {value: "Dog"},
        {value: "Cat"}
    ]},
    {value: "Plant"}
]};

React.render(
    <Tree tree={treeOfLife}/>,
    document.getElementById('tree'));

Screenshot of the result:

Answer 2

Here's another approach, courtesy of jethrolarson on GitHub:

Given the recursive component Tree

import React from 'react';

const Tree = ({treeData}) => (
    <div>
        {treeData.nodeName}{' '}
        {treeData.children.map(subTree => (
            <Tree treeData={subTree} />
        ))}
    </div>
);

that takes a tree data structure like the one below

                Root
                /  \
           Child1   Child2
          /     \        \
     GChild1   GChild2   GChild3

(as code:

const treeData = {
    nodeName: "Root",
    children: [
        {
            nodeName: "Child1",
            children: [
                {nodeName: "GChild1"},
                {nodeName: "GChild2"},
            ]
        },
        {
            nodeName: "Child2",
            children: [
                {nodeName: "GChild3"},
            ]
        },
    ]
};

),

the propTypes for Tree can be defined as:

import PropTypes from 'prop-types';

const treeDataShape = {
    nodeName: PropTypes.string.isRequired,
};
treeDataShape.children = PropTypes.arrayOf(PropTypes.shape(treeDataShape));

Tree.propTypes = {
    treeData: PropTypes.shape(treeDataShape),
};

Note how all of the references to treeDataShape refer to the same object. Defining children after the object is created lets you recursively reference the same object.