开发过程中的对象冻结

Question

Please see the code here

if (process.env.NODE_ENV !== 'production') {
    if ('function' === typeof Object.freeze) {
        Object.keys(self._routes).forEach(function freezeRoute(name) {
            var route = self._routes[name];
            Object.freeze(route.config);
            Object.freeze(route.keys);
            Object.freeze(route);
        });
        Object.freeze(self._routes);
    }
}

why do freeze in non production mode. Is it to verify it is not being modified during development, but avoid any kind of runtime cost during production?

Answer 1

Yes, this is precisely the reason mentioned in the commit where this functionality was added :

We use Object.freeze to freeze the router and route objects for non-production environments to ensure the immutability of these objects.

For production environments, it is recommended to use tools like envify along with uglify as part of your build process to strip out the [non-]production specific code for performance benefits.

We use if (process.env.NODE_ENV !== 'production') to wrap around Object.freeze() , so that you can use various tools to build the code for different environments:

The reason they did this was because Object.freeze was slow at the time - at this point the performance hit of Object.freeze has been greatly mitigated ( at least in V8 ).