Attempt to implement the RouteResolver API out of core

mithril-route-resolver.js

// This wraps the `m.route` API to implement route resolvers
//
// Note: this is all in pure ES5
//
// Assumed extensions:
// - `m.route.default()` - Get the default route

var route = (function () {
    "use strict"
    
    var changed = true

    function route(elem, defaultRoute, routes) {
        function onchange(vnode) {
            if (!changed) return
            changed = false
            var matcher = routes[m.route.get()]
            function set(comp) {
                vnode.state.comp = comp || "div"
                vnode.state.render = typeof matcher.render === "function"
            }
            function bail(e) {
                m.route.set(m.route.default(), null, {replace: true})
                throw e
            }
            try {
                if (
                    matcher == null || typeof matcher !== "object" ||
                    typeof matcher.onmatch !== "function"
                ) {
                    vnode.state.comp = matcher
                    vnode.state.render = typeof matcher.render === "function"
                } else {
                    var request = vnode.attrs.onmatch(vnode.attrs, m.route.get())
                    if (request == null || typeof request.then !== "function") {
                        set(request)
                    } else {
                        Promise.resolve(request).then(set, bail).then(m.redraw)
                    }
                }
            } catch (e) {
                bail(e)
            }
        }

        var RouteResolver = {
            oninit: onchange,
            onupdate: onchange,

            view: function (vnode) {
                if (vnode.state.comp == null) return []
                if (!vnode.state.render) return m(vnode.state.comp, vnode.attrs)
                return vnode.attrs.render(m(vnode.state.comp, vnode.attrs))
            }
        }

        var wrapped = Object.create(null)

        Object.keys(routes).forEach(function (route) {
            wrapped[route] = RouteResolver
        })

        return m.route(elem, defaultRoute, wrapped)
    }
    
    Object.keys(m.route).forEach(function (key) {
        route[key] = m.route[key]
    })

    route.set = function (route, params, opts) {
        changed = true
        return m.route.set(route, params, opts)
    }
    
    return route
})()