React mixin for caching state in sessionStorage across mounts.

react-state-cache-mixin.js

var StateCacheMixin = function(key) {
    if (!Modernizr.sessionstorage) {
        return {};
    }
    return {
        componentWillMount: function() {
            var prevState = sessionStorage.getItem(key);
            if (prevState === null) return;
            try {
                prevState = JSON.parse(prevState);
            }
            catch (e) {
                return;
            }
            if (typeof prevState === 'object') {
                this.setState(prevState);
            }
        },
        componentWillUnmount: function() {
            if (this.state !== undefined) {
                sessionStorage.setItem(key, JSON.stringify(this.state));
            }
        }
    };
};

Things I don't like: can't use session-stored variables in componentWillMount (as the mixin method apparently gets called after the component), no granularity in choosing which properties to store.