element-web/src/Velociraptor.js

import React from "react";
import ReactDom from "react-dom";
import Velocity from "velocity-animate";
import PropTypes from 'prop-types';

/**
 * The Velociraptor contains components and animates transitions with velocity.
 * It will only pick up direct changes to properties ('left', currently), and so
 * will not work for animating positional changes where the position is implicit
 * from DOM order. This makes it a lot simpler and lighter: if you need fully
 * automatic positional animation, look at react-shuffle or similar libraries.
 */
export default class Velociraptor extends React.Component {
    static propTypes = {
        // either a list of child nodes, or a single child.
        children: PropTypes.any,

        // optional transition information for changing existing children
        transition: PropTypes.object,

        // a list of state objects to apply to each child node in turn
        startStyles: PropTypes.array,

        // a list of transition options from the corresponding startStyle
        enterTransitionOpts: PropTypes.array,
    };

    static defaultProps = {
        startStyles: [],
        enterTransitionOpts: [],
    };

    constructor(props) {
        super(props);

        this.nodes = {};
        this._updateChildren(this.props.children);
    }

    componentDidUpdate() {
        this._updateChildren(this.props.children);
    }

    _updateChildren(newChildren) {
        const oldChildren = this.children || {};
        this.children = {};
        React.Children.toArray(newChildren).forEach((c) => {
            if (oldChildren[c.key]) {
                const old = oldChildren[c.key];
                const oldNode = ReactDom.findDOMNode(this.nodes[old.key]);

                if (oldNode && oldNode.style.left !== c.props.style.left) {
                    Velocity(oldNode, { left: c.props.style.left }, this.props.transition).then(() => {
                        // special case visibility because it's nonsensical to animate an invisible element
                        // so we always hidden->visible pre-transition and visible->hidden after
                        if (oldNode.style.visibility === 'visible' && c.props.style.visibility === 'hidden') {
                            oldNode.style.visibility = c.props.style.visibility;
                        }
                    });
                    //console.log("translation: "+oldNode.style.left+" -> "+c.props.style.left);
                }
                if (oldNode && oldNode.style.visibility === 'hidden' && c.props.style.visibility === 'visible') {
                    oldNode.style.visibility = c.props.style.visibility;
                }
                // clone the old element with the props (and children) of the new element
                // so prop updates are still received by the children.
                this.children[c.key] = React.cloneElement(old, c.props, c.props.children);
            } else {
                // new element. If we have a startStyle, use that as the style and go through
                // the enter animations
                const newProps = {};
                const restingStyle = c.props.style;

                const startStyles = this.props.startStyles;
                if (startStyles.length > 0) {
                    const startStyle = startStyles[0];
                    newProps.style = startStyle;
                    // console.log("mounted@startstyle0: "+JSON.stringify(startStyle));
                }

                newProps.ref = ((n) => this._collectNode(
                    c.key, n, restingStyle,
                ));

                this.children[c.key] = React.cloneElement(c, newProps);
            }
        });
    }

    _collectNode(k, node, restingStyle) {
        if (
            node &&
            this.nodes[k] === undefined &&
            this.props.startStyles.length > 0
        ) {
            const startStyles = this.props.startStyles;
            const transitionOpts = this.props.enterTransitionOpts;
            const domNode = ReactDom.findDOMNode(node);
            // start from startStyle 1: 0 is the one we gave it
            // to start with, so now we animate 1 etc.
            for (var i = 1; i < startStyles.length; ++i) {
                Velocity(domNode, startStyles[i], transitionOpts[i-1]);
                /*
                console.log("start:",
                            JSON.stringify(transitionOpts[i-1]),
                            "->",
                            JSON.stringify(startStyles[i]),
                            );
                */
            }

            // and then we animate to the resting state
            Velocity(domNode, restingStyle,
                transitionOpts[i-1])
                .then(() => {
                    // once we've reached the resting state, hide the element if
                    // appropriate
                    domNode.style.visibility = restingStyle.visibility;
                });

            // console.log("enter:",
            //             JSON.stringify(transitionOpts[i-1]),
            //             "->",
            //             JSON.stringify(restingStyle));
        }
        this.nodes[k] = node;
    }

    render() {
        return (
            <span>
                { Object.values(this.children) }
            </span>
        );
    }
}