Mar 8, 2023
MelbJS March 2023 notes
Raw notes from the MelbJS meetup held at Culture Amp in Richmond on 8 March, 2023.
Fundamentals of Module Federation, Mathew ByrnePermalink to Fundamentals of Module Federation, Mathew Byrne
- Scaling build times
- Dependency versioning: Team A wants to upgrade React, Team B isn’t ready
- Deployments: slow builds means deploys back up
- In general, bottlenecks!
- Compromised user experience
- Hard to maintain client state across apps
- Scaling challenges still exist within each app
- Duplicate dependencies
- No on-demand loading of code. All dependencies must be available first.
- Manual juggling of those dependencies.
- Performance: round-tripping of cascading requests for dependencies.
- Limited client support.
- Can’t use non-ESM dependencies.
- Host: The first webpack runtime to boot on the client
- Remote: A bundle that the host can dynamically load in when requested.
- These are not mutually exclusive.
ModuleFederationPluginthat declares a remote for
App2. App2’s webpack config has a
ModuleFederationPluginthat declares that App2 is remote that can be loaded by a host. When App1 loads App2, App2 gets its react, etc. from App1. A bundle can be both a host and a remote, which enables some interesting configurations. The module federation project repo has dozens of examples. E.g. Bidirectional, two modules that can each act as a host, but load the other on demand. App Shell, a single host designed to load multiple remotes. MF first shipped with Webpack 5 in Oct 2020. Next 13, SSR support are now there. Delegate modules, a new feature like middleware for loading remotes (e.g. dynamic host selection, etc.), just landed. Further reading:
- Follow Zack Jackson, @ScriptedAlchemy.
Standard Promises. Promise Standards, FrankyPermalink to Standard Promises. Promise Standards, Franky
How it works (according to the spec):
- Check that the
Promiseconstructor was passed a function as an executor.
- Create an internal promise object, using the Promise prototype, which includes all the promise features we’re used to (
then, etc.). Creates some internal “slots” for information about the promise.
- Create the
rejectfunctions, which are passed into the executor later.
- Call the executor function. If it completes successfully, it’s a normal completion. If it throws and exception, it’s an abrupt completion.
- Return the promise!
reject) work internally: Depending which is called, the promise will be fulfilled or rejected. If
resolveis called with another promise, that promise is used in turn to continue resolving. Otherwise, the promise is resolved straight away. How a promise is fulfilled:
thenmethod. The specification for this function is really, really long! For brevity, we’ll ignore all the parts that have to do with rejecting. This is where the HTML spec starts to come in. The
thenmethod creates another promise, which operates just like the one we’ve been talking about. It’s a bit hidden, but it’s what lets us chain promises.
thentakes a callback, which gets passed to
- Event loop
- Task queue
- Microtask queue
HostEnqueuePromiseJobschedules tasks on the high-priority microtask queue (defined in the HTML spec). Another example of how these two standards operate together:
HostCallJobCallback. Not covered for time (but equally interesting!): stuff like what happens if
resolveis passed another promise. Opens up another can of worms. Also interesting, how browser APIs like
fetchwork under the surface.
Pyodide and JS: The One Language to Rule Them All, Hon Weng ChongPermalink to Pyodide and JS: The One Language to Rule Them All, Hon Weng Chong
May 24, 2006
Jules has whipped up this sexy Google Maps mashup for sharing bike routes.
Jan 11, 2006
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