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networks/packets-why-the-internet-cuts-your-message-into-numbered-pieces.md Packets: why the internet cuts your message into numbered pieces When you send a message online, it never travels as one block. The internet cuts it into small packets, each with a label saying where it… 5 min read · 5 Oct web/what-is-json-edit-it-live-and-see-why-apis-are-so-strict-about-it.md What is JSON? Edit it live and see why APIs are so strict about it When an app asks a server for data, the reply has to travel as plain text. JSON is the format most web APIs use: six kinds of value… 5 min read · 4 Oct mobile/two-phones-one-note-what-happens-when-edits-collide-offline.md Two phones, one note: what happens when edits collide offline? Phones lose signal all the time, so good apps keep a local copy of your data and sync with a server later. But what happens when two… 5 min read · 3 Oct software-design/your-first-unit-test-catch-the-leap-year-bug-a-quick-check-misses.md Your first unit test: catch the leap-year bug a quick check misses A unit test is a tiny piece of code that checks another piece of code: you pick an input, write down the answer you expect, and let the… 5 min read · 3 Oct infrastructure/what-is-ci-the-robot-that-tests-your-code-every-time-you-push.md What is CI? The robot that tests your code every time you push You change one line, it looks fine, and two days later something far away breaks. Continuous integration (CI) is a robot that prevents… 5 min read · 2 Oct computer-science/what-is-an-algorithm-watch-two-recipes-race-to-sort-six-bars.md What Is an Algorithm? Watch Two Recipes Race to Sort Six Bars An algorithm is a recipe so precise that someone who doesn't understand the goal could still follow it and get the right answer. Computers… 10 min read · 1 Oct mobile/native-web-or-cross-platform-how-apps-get-from-your-code-to-a-phone.md Native, web or cross-platform? How apps get from your code to a phone Every app idea hits the same fork in the road. Build it native in Swift for iPhone and Kotlin for Android, build it for the web with HTML… 9 min read · 1 Oct infrastructure/from-localhost-to-production-what-deploying-your-code-really-means.md From localhost to production: what “deploying” your code really means Your app runs perfectly at localhost:3000, but the link does nothing on a friend's phone. That's because localhost means "this computer"… 10 min read · 1 Oct languages/why-does-my-javascript-loop-run-one-time-too-many.md Why does my JavaScript loop run one time too many? A loop tells JavaScript to repeat some code until a condition says stop. A for loop packs three pieces onto one line: a setup that runs… 8 min read · 1 Oct networks/ip-addresses-and-ports-the-street-address-and-the-apartment-number.md IP addresses and ports: the street address and the apartment number Every message on a network needs two things to arrive: an IP address to find the right computer, and a port to find the right program on… 10 min read · 1 Oct networks/how-does-example-com-turn-into-an-ip-address-dns-step-by-step.md How does example.com turn into an IP address? DNS, step by step Computers find each other by number, not by name. Before your browser can load example.com, it has to find the site's IP address, and… 11 min read · 1 Oct computers/counting-with-only-0-and-1-how-computers-store-numbers-and-letters.md Counting with Only 0 and 1: How Computers Store Numbers and Letters Every photo, message and web page on your computer is stored as numbers written with just two digits: 0 and 1. That's binary, and it works… 9 min read · 1 Oct