{"rowid": 294, "title": "New Tricks for an Old Dog", "contents": "Much of my year has been spent helping new team members find their way around the expansive and complex codebase that is the TweetDeck front-end, trying to build a happy and productive group of people around a substantial codebase with many layers of legacy.\nI\u2019ve loved doing this. Everything from writing new documentation, drawing diagrams, and holding technical architecture sessions teaches you something you didn\u2019t know or exposes an area of uncertainty that you can go work on.\nIn this article, I hope to share some experiences and techniques that will prove useful in your own situation and that you can impress your friends in some new and exciting ways!\nHow do you do, fellow kids?\nTo start with I\u2019d like to introduce you to our JavaScript framework, Flight. Right now it\u2019s used by twitter.com and TweetDeck although, as a company, Twitter is largely moving to React.\nOver time, as we used Flight for more complex interfaces, we found it wasn\u2019t scaling with us.\nComposing components into trees was fiddly and often only applied for a specific parent-child pairing. It seems like an obvious feature with hindsight, but it didn\u2019t come built-in to Flight, and it made reusing components a real challenge.\nThere was no standard way to manage the state of a component; they all did it slightly differently, and the technique often varied by who was writing the code. This cost us in maintainability as you just couldn\u2019t predict how a component would be built until you opened it.\nMaking matters worse, Flight relied on events to move data around the application. Unfortunately, events aren\u2019t good for giving structure to complex logic. They jump around in a way that\u2019s hard to understand and debug, and force you to search your code for a specific string \u2014 the event name\u201a to figure out what\u2019s going on.\nTo find fixes for these problems, we looked around at other frameworks. We like React for it\u2019s simple, predictable state management and reactive re-render flow, and Elm for bringing strict functional programming to everyone.\nBut when you have lots of existing code, rewriting or switching framework is a painful and expensive option. You have to understand how it will interact with your existing code, how you\u2019ll test it alongside existing code, and how it will affect the size and performance of the application. This all takes time and effort!\nInstead of planning a rewrite, we looked for the ideas hidden within other frameworks that we could reapply in our own situation or bring to the tools we already were using.\nBoiled down, what we liked seemed quite simple:\n\nComponent nesting & composition\nEasy, predictable state management\nNormal functions for data manipulation\n\nMaking these ideas applicable to Flight took some time, but we\u2019re in a much better place now. Through persistent trial-and-error, we have well documented, testable and standard techniques for creating complex component hierarchies, updating and reacting to state changes, and passing data around the app.\nWhile the specifics of our situation and Flight aren\u2019t really important, this experience taught me something: \n\nDistill good tech into great ideas. You can apply great ideas anywhere.\n\nYou don\u2019t have to use cool kids\u2019 latest framework, hottest build tool or fashionable language to benefit from them. If you can identify a nugget of gold at the heart of it all, why not use it to improve what you have already?\nTimes, they are a changin\u2019\nApart from stealing ideas from the new and shiny, how can we keep make the most of improved tooling and techniques? Times change and so should the way we write code.\nGoing back in time a bit, TweetDeck used some slightly outmoded tools for building and bundling. Without a transpiler like Babel we were missing out new language features, and without a more advanced build tools like Webpack, every module\u2019s source was encased in AMD boilerplate.\nIn fact, we found ourselves with a mix of both AMD syntaxes:\ndefine([\"lodash\"], function (_) {\n  // . . .\n});\n\ndefine(function (require) {\n  var _ = require(\"lodash\");\n  // . . .\n});\nThis just wouldn\u2019t do. And besides, what we really wanted was CommonJS, or even ES2015 module syntax:\nimport _ from \"lodash\";\nThese days we\u2019re using Babel, Webpack, ES2015 modules and many new language features that make development just\u2026 better. But how did we get there?\nTo explain, I want to introduce you to codemods and jscodeshift.\nA codemod is a large-scale refactor of a whole codebase, often mechanical or repetitive. Think of renaming a module or changing an API like URL(\"...\") to new URL(\"...\").\njscodeshift is a toolkit for running automated codemods, where you express a code transformation using code. The automated codemod operates on each file\u2019s syntax tree \u2013 a data-structure representation of the code \u2014 finding and modifying in place as it goes.\nHere\u2019s an example that renames all instances of the variable foo to bar:\nmodule.exports = function (fileInfo, api) {\n  return api\n    .jscodeshift(fileInfo.source)\n    .findVariableDeclarators('foo')\n    .renameTo('bar')\n    .toSource();\n};\nIt\u2019s a seriously powerful tool, and we\u2019ve used it to write a series of codemods that:\n\nrename modules,\nunify our use of AMD to a single syntax,\ntransition from one testing framework to another, and\nswitch from AMD to CommonJS.\n\nThese changes can be pretty huge and far-reaching. Here\u2019s an example commit from when we switched to CommonJS:\ncommit 8f75de8fd4c702115c7bf58febba1afa96ae52fc\nDate:   Tue Jul 12 2016\n\n   Run AMD -> CommonJS codemod\n\n 418 files changed, 47550 insertions(+), 48468 deletions(-)\n\nYep, that\u2019s just under 50k lines changed, tested, merged and deployed without any trouble. AMD be gone!\n\nFrom this step-by-step approach,  using codemods to incrementally tweak and improve, we extracted a little codemod recipe for making significant, multi-stage changes:\n\nFind all the existing patterns\nChoose the two most similar\nUnify with a codemod\nRepeat.\n\nFor example:\n\nFor module loading, we had 2 competing AMD patterns plus some use of CommonJS\nThe two AMD syntaxes were the most similar\nWe used a codemod to move to unify the AMD patterns\nLater we returned to AMD to convert it to CommonJS\n\nIt\u2019s worked for us, and if you\u2019d like to know more about codemods then check out Evolving Complex Systems Incrementally by Facebook engineer, Christoph Pojer.\nWelcome aboard!\nAs TweetDeck has gotten older and larger, the amount of things a new engineer has to learn about has exploded. The myriad of microservices that manage our data and their layers of authentication, security and business logic around them make for an overwhelming amount of information to hand to a newbie.\nInspired by Amy\u2019s amazing Guide to the Care and Feeding of Junior Devs, we realised it was important to take time to design our onboarding that each of our new hires go through to make the most of their first few weeks.\nJoining a new company, team, or both, is stressful and uncomfortable. Everything you can do to help a new hire will be valuable to them. So please, take time to design your onboarding!\nAnd as you build up an onboarding process, you\u2019ll create things that are useful for more than just new hires; it\u2019ll force you to write documentation, for example, in a way that\u2019s understandable for people who are unfamiliar with your team, product and codebase. This can lead to more outside contributions: potential contributors feel more comfortable getting set up on your product without asking for help.\nThis is something that\u2019s taken for granted in open source, but somehow I think we forget about it in big companies.\nAfter all, better documentation is just a good thing. You will forget things from time to time, and you\u2019d be surprised how often the \u201cbeginner\u201d docs help!\nFor TweetDeck, we put together system and architecture diagrams, and one-pager explanations of important concepts:\n\nWhat are our dependencies?\nWhere are the potential points of failure?\nWhere does authentication live? Storage? Caching?\nWho owns \u201cX\u201d?\n\n\nOf course, learning continues long after onboarding. The landscape is constantly shifting; old services are deprecated, new APIs appear and what once true can suddenly be very wrong. Keeping up with this is a serious challenge, and more than any one person can track.\nTo address this, we\u2019ve thought hard about our knowledge sharing practices across the whole team. For example, we completely changed the way we do code review.\nIn my opinion, code review is the single most effective practice you can introduce to share knowledge around, and build the quality and consistency of your team\u2019s work. But, if you\u2019re not doing it, here\u2019s my suggestion for getting started:\n\nEvery pull request gets a +1 from someone else.\n\nThat\u2019s all \u2014 it\u2019s very light-weight and easy. Just ask someone to have a quick look over your code before it goes into master.\nAt Twitter, every commit gets a code review. We do a lot of reviewing, so small efficiency and effectiveness improvements make a big difference. Over time we learned some things:\n\nDon\u2019t review for more than hour 1\nKeep reviews smaller than ~400 lines 2\nCode review your own code first 2\n\nAfter an hour, and above roughly 400 lines, your ability to detect issues in a code review starts to decrease. So review little and often. The gaps around lunch, standup and before you head home are ideal. And remember, if someone\u2019s put code up for a review, that review is blocking them doing other work. It\u2019s your job to unblock them.\nOn TweetDeck, we actually try to keep reviews under 250 lines. It doesn\u2019t sound like much, but this constraint applies pressure to make smaller, incremental changes. This makes breakages easier to detect and roll back, and leads to a very natural feature development process that encourages learning and iteration.\nBut the most important thing I\u2019ve learned personally is that reviewing my own code is the best way to spot issues. I try to approach my own reviews the way I approach my team\u2019s: with fresh, critical eyes, after a break, using a dedicated code review tool.\nIt\u2019s amazing what you can spot when you put a new in a new interface around code you\u2019ve been staring at for hours!\nAnd yes, this list features science. The data backs up these conclusions, and if you\u2019d like to learn more about scientific approaches to software engineering then I recommend you buy Making Software: What Really Works, and Why We Believe It. It\u2019s ace.\nFor more dedicated information sharing, we\u2019ve introduced regular seminars for everyone who works on a specific area or technology. It works like this: a team-member shares or teaches something to everyone else, and next time it\u2019s someone else\u2019s turn. Giving everyone a chance to speak, and encouraging a wide range of topics, is starting to produce great results.\nIf you\u2019d like to run a seminar, one thing you could try to get started: run a point at the thing you least understand in our architecture session \u2014 thanks to James for this idea. And guess what\u2026 your onboarding architecture diagrams will help (and benefit from) this!\nMore, please!\nThere\u2019s a few ideas here to get you started, but there are even more in a talk I gave this year called Frontend Archaeology, including a look at optimising for confidence with front-end operations.\nAnd finally, thanks to Amy for proof reading this and to Passy for feedback on the original talk.\n\n\n\n\nDunsmore et al. 2000. Object-Oriented Inspection in the Face of Delocalisation. Beverly, MA: SmartBear Software.\u00a0\u21a9\n\n\nCohen, Jason. 2006. Best Kept Secrets of Peer Code Review. Proceedings of the 22nd ICSE 2000: 467-476.\u00a0\u21a9 \u21a9", "year": "2016", "author": "Tom Ashworth", "author_slug": "tomashworth", "published": "2016-12-18T00:00:00+00:00", "url": "https://24ways.org/2016/new-tricks-for-an-old-dog/", "topic": "code"}