crgeary/inertia.js

## inertia.js
const lodashPick = (object, keys) => {
    return keys.reduce((obj, key) => {
        if (object && object.hasOwnProperty(key)) {
            obj[key] = object[key];
        }
        return obj;
    }, {});
};

const setupProps = async (props) => {
    const _props = { ...props };
    for (i in _props) {
        if (typeof _props[i] === "object") {
            _props[i] = await setupProps(_props[i]);
        } else if (typeof _props[i] === "function") {
            _props[i] = await _props[i].call();
        }
    }
    return _props;
};

const getRequestedProps = (req, component, props) => {
    const requestedProps = req.header("X-Inertia-Partial-Data");
    if (requestedProps) {
        if (req.header("X-Inertia-Partial-Component") === component) {
            return lodashPick(props, requestedProps.split(","));
        }
    }
    return props;
};

const shouldSeeOther = (req, res) => {
    const methods = ["PUT", "PATCH", "DELETE"];
    return res.statusCode === 303 && methods.includes(req.method);
};

const shouldConflict = (req, version) => {
    return req.method === `GET` && req.header("X-Inertia-Version") !== version;
};

const inertia = (options = {}) => {
    options = {
        version: null,
        view: "app",
        ...options,
    };

    return (req, res, next) => {
        res.inertia = async (component, inertiaProps, viewProps) => {
            const url = `${req.protocol}://${req.get("host")}${
                req.originalUrl
            }`;
            const props = getRequestedProps(req, component, inertiaProps);
            const inertiaObject = {
                component: component,
                props: await setupProps(props),
                url: url,
                version: options.version,
            };

            if (!req.header("X-Inertia")) {
                return res.render(options.view, {
                    layout: false,
                    page: JSON.stringify(inertiaObject),
                    ...viewProps,
                });
            }

            if (shouldConflict(req, options.version)) {
                if (req.session && typeof req.flash === "function") {
                    const messages = req.flash();
                    for (message in messages) {
                        req.flash(message, messages[message]);
                    }
                }
                res.setHeader("X-Inertia-Location", url);
                return res.status(409).end();
            }

            res.setHeader("Vary", "Accept");
            res.setHeader("X-Inertia", "true");
            res.setHeader("X-Inertia-Version", options.version);

            return res.json(inertiaObject);
        };

        const end = res.end;
        res.end = function () {
            if (shouldSeeOther(req, res)) {
                res.status(303);
            }
            return end.apply(this, arguments);
        };
        next();
    };
};

exports.inertia = inertia;

## server.js
const express = require("express");
const session = require("express-session");
const flash = require("connect-flash");

const { inertia } = require("./inertia");

const app = express();

app.engine("hbs", hbs.engine);
app.set("view engine", "hbs");

app.use(
    session({
        secret: "@todo assign a secret",
        resave: false,
        saveUninitialized: false,
        cookie: {
            maxAge: 1000 * 15,
        },
    })
);

app.use(flash());

app.use(
    inertia({
        view: "app",
        version: "@todo webpack manifest hash (for example)",
    })
);

app.get("/", async (req, res) => {
    res.inertia("Dashboard", {
        title: "Dashboard!",
        reports: async () => {
            return await aTimeConsumingTasksLikeDatabaseAccess();
        }
    });
});

app.listen(3000, () => {
    console.log("Listening at http://localhost:3000");
});

## views-app.hbs
<!DOCTYPE html>
<html lang="en-gb">

<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>App</title>
</head>
<body>

    <div id="app" data-page="{{ page }}"></div>

    <script src="/app.js"></script>

</body>
</html>
	const lodashPick = (object, keys) => {
	return keys.reduce((obj, key) => {
	if (object && object.hasOwnProperty(key)) {
	obj[key] = object[key];
	}
	return obj;
	}, {});
	};

	const setupProps = async (props) => {
	const _props = { ...props };
	for (i in _props) {
	if (typeof _props[i] === "object") {
	_props[i] = await setupProps(_props[i]);
	} else if (typeof _props[i] === "function") {
	_props[i] = await _props[i].call();
	}
	}
	return _props;
	};

	const getRequestedProps = (req, component, props) => {
	const requestedProps = req.header("X-Inertia-Partial-Data");
	if (requestedProps) {
	if (req.header("X-Inertia-Partial-Component") === component) {
	return lodashPick(props, requestedProps.split(","));
	}
	}
	return props;
	};

	const shouldSeeOther = (req, res) => {
	const methods = ["PUT", "PATCH", "DELETE"];
	return res.statusCode === 303 && methods.includes(req.method);
	};

	const shouldConflict = (req, version) => {
	return req.method === `GET` && req.header("X-Inertia-Version") !== version;
	};

	const inertia = (options = {}) => {
	options = {
	version: null,
	view: "app",
	...options,
	};

	return (req, res, next) => {
	res.inertia = async (component, inertiaProps, viewProps) => {
	const url = `${req.protocol}://${req.get("host")}${
	req.originalUrl
	}`;
	const props = getRequestedProps(req, component, inertiaProps);
	const inertiaObject = {
	component: component,
	props: await setupProps(props),
	url: url,
	version: options.version,
	};

	if (!req.header("X-Inertia")) {
	return res.render(options.view, {
	layout: false,
	page: JSON.stringify(inertiaObject),
	...viewProps,
	});
	}

	if (shouldConflict(req, options.version)) {
	if (req.session && typeof req.flash === "function") {
	const messages = req.flash();
	for (message in messages) {
	req.flash(message, messages[message]);
	}
	}
	res.setHeader("X-Inertia-Location", url);
	return res.status(409).end();
	}

	res.setHeader("Vary", "Accept");
	res.setHeader("X-Inertia", "true");
	res.setHeader("X-Inertia-Version", options.version);

	return res.json(inertiaObject);
	};

	const end = res.end;
	res.end = function () {
	if (shouldSeeOther(req, res)) {
	res.status(303);
	}
	return end.apply(this, arguments);
	};
	next();
	};
	};

	exports.inertia = inertia;
	const express = require("express");
	const session = require("express-session");
	const flash = require("connect-flash");

	const { inertia } = require("./inertia");

	const app = express();

	app.engine("hbs", hbs.engine);
	app.set("view engine", "hbs");

	app.use(
	session({
	secret: "@todo assign a secret",
	resave: false,
	saveUninitialized: false,
	cookie: {
	maxAge: 1000 * 15,
	},
	})
	);

	app.use(flash());

	app.use(
	inertia({
	view: "app",
	version: "@todo webpack manifest hash (for example)",
	})
	);

	app.get("/", async (req, res) => {
	res.inertia("Dashboard", {
	title: "Dashboard!",
	reports: async () => {
	return await aTimeConsumingTasksLikeDatabaseAccess();
	}
	});
	});

	app.listen(3000, () => {
	console.log("Listening at http://localhost:3000");
	});
	<!DOCTYPE html>
	<html lang="en-gb">

	<head>
	<meta charset="utf-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>App</title>
	</head>
	<body>

	<div id="app" data-page="{{ page }}"></div>

	<script src="/app.js"></script>

	</body>
	</html>