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mobile/how-does-a-push-notification-find-your-phone-when-the-app-is-closed.md How does a push notification find your phone when the app is closed? A push notification does not come from your app. Your phone keeps one connection to a service run by Apple or Google, and your app's server… 5 min read · 6 Oct 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 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 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 security/how-websites-check-your-password-without-ever-storing-it.md How websites check your password without ever storing it A well-built website never saves your password. It saves a hash: a fixed-size fingerprint that's quick to compute and impossible to run… 9 min read · 1 Oct ai/machine-learning-by-example-how-a-computer-learns-apples-from-oranges.md Machine learning by example: how a computer learns apples from oranges Normal programs follow rules a person wrote. Machine learning turns that around: you give the computer examples with the right answers, and… 11 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 computer-science/linear-vs-binary-search-why-30-guesses-can-beat-a-billion.md Linear vs binary search: why 30 guesses can beat a billion Need to find one item in a list? You can check every item in turn (linear search), or, if the list is sorted, look at the middle and throw… 10 min read · 1 Oct web/html-tags-how-angle-brackets-become-a-tree-in-your-browser.md HTML tags: how angle brackets become a tree in your browser Every web page is plain text with labels in angle brackets: HTML tags. An opening tag, some content and a closing tag make an element, and… 13 min read · 1 Oct software-design/functions-why-you-should-stop-copy-pasting-your-code.md Functions: Why You Should Stop Copy-Pasting Your Code Copy-pasting code works fine on the day you do it. It fails the day you need to change it, and have to find and fix every copy without… 9 min read · 1 Oct ai/how-a-chatbot-writes-one-guessed-word-at-a-time.md How a chatbot writes: one guessed word at a time A chatbot doesn't plan its reply and then type it out. It repeats one small step: look at the text so far, give every possible next token… 12 min read · 1 Oct