Today I Learned

A collection of useful things I’ve picked up along the way.

Shell & Terminal

• cd with no args takes you to your home directory.
• cd - takes you to the previous directory.
• !! repeats the last command. Useful with sudo !!.
• !$ refers to the last argument of the previous command.
• ctrl+r lets you search through command history.
• ctrl+a moves cursor to start of line, ctrl+e to end.
• ctrl+u clears everything before the cursor.
• ctrl+k clears everything after the cursor.
• ctrl+w deletes the word before the cursor.
• alt+. inserts the last argument from the previous command.
• pbcopy and pbpaste on macOS let you use the clipboard from terminal.
• cat file | pbcopy copies file contents to clipboard.
• open . on macOS opens Finder in the current directory.
• command -v checks if a command exists (portable alternative to which).
• Wrapping a command in $() captures its output: echo "Today is $(date)".
• && runs the next command only if the previous succeeded.
• || runs the next command only if the previous failed.
• ; runs commands sequentially regardless of success/failure.
• > file overwrites, >> file appends.
• 2>&1 redirects stderr to stdout.
• tee writes to both stdout and a file: command | tee output.txt.
• watch -n 2 command runs a command every 2 seconds.
• time command shows how long a command takes to run.
• history | grep pattern searches your command history.
• fc opens your last command in an editor.
• jobs lists background processes, fg brings one to foreground.
• nohup command & keeps a process running after terminal closes.
• disown detaches a running job from the terminal.

Git

• git checkout - checks out the previous branch.
• git switch - also switches to the previous branch (newer syntax).
• git stash saves uncommitted changes for later.
• git stash pop applies and removes the most recent stash.
• git stash list shows all stashes.
• git stash show -p shows the diff of the most recent stash.
• git diff --staged shows changes that are staged for commit.
• git log --oneline shows compact commit history.
• git log --graph --oneline --all visualises branch history.
• git blame file shows who changed each line and when.
• git show commit:file shows a file at a specific commit.
• git cherry-pick commit applies a single commit to current branch.
• git rebase -i HEAD~3 lets you edit the last 3 commits.
• git commit --amend updates the last commit.
• git reset HEAD~1 undoes the last commit, keeping changes.
• git reset --hard HEAD~1 undoes the last commit, discarding changes.
• git reflog shows history of HEAD movements (useful for recovery).
• git clean -fd removes untracked files and directories.
• git bisect helps find which commit introduced a bug.
• git worktree lets you check out multiple branches simultaneously.
• git shortlog -sn shows commit count per author.
• git config --global alias.co checkout creates command aliases.
• git diff --word-diff shows inline word-level diffs.
• git log -p -- file shows the history of changes to a specific file.
• git remote -v shows remote repository URLs.
• git fetch --prune removes references to deleted remote branches.

JavaScript & TypeScript

• Array.at(-1) gets the last element of an array.
• ?? (nullish coalescing) only falls back for null or undefined, not falsy values.
• ?. (optional chaining) safely accesses nested properties.
• Object.fromEntries() converts an array of key-value pairs to an object.
• structuredClone() creates a deep copy of an object.
• Array.from({ length: 5 }, (_, i) => i) creates [0, 1, 2, 3, 4].
• Destructuring with defaults: const { name = 'Anonymous' } = user.
• Promise.allSettled() waits for all promises regardless of rejection.
• AbortController can cancel fetch requests and other async operations.
• new Set([...arr]) removes duplicates from an array.
• Object.hasOwn(obj, prop) is safer than obj.hasOwnProperty(prop).
• Template literals support tagged templates for custom processing.
• for...of iterates values, for...in iterates keys (usually avoid for...in).
• globalThis works in browsers, Node, and workers.
• queueMicrotask() schedules code to run after current task but before rendering.
• Arrow functions don’t have their own this, arguments, or super.
• Number.isNaN() is stricter than global isNaN().
• Object.freeze() makes an object immutable (shallow only).
• Reflect.ownKeys() returns all keys including symbols.
• new URL() and URLSearchParams make URL manipulation much easier.

CSS

• aspect-ratio: 16/9 maintains element proportions without padding hacks.
• gap works in flexbox, not just grid.
• min(), max(), and clamp() enable responsive values without media queries.
• scroll-behavior: smooth enables smooth scrolling site-wide.
• scroll-margin-top offsets scroll position for fixed headers.
• ::marker pseudo-element styles list bullets.
• :is() and :where() reduce selector repetition.
• :has() is a parent selector (finally!).
• inset: 0 is shorthand for top: 0; right: 0; bottom: 0; left: 0.
• place-items: center centres in both directions (grid/flexbox).
• isolation: isolate creates a new stacking context.
• accent-color styles form controls like checkboxes.
• color-scheme: light dark tells the browser your site supports both modes.
• prefers-reduced-motion media query respects user accessibility settings.
• content-visibility: auto can significantly improve rendering performance.
• text-wrap: balance creates more visually balanced text wrapping.

Node.js

• node --watch file.js auto-restarts on file changes (Node 18+).
• npm pkg get version prints the package version.
• npm outdated shows packages that need updating.
• npm ls shows the dependency tree.
• npm why package explains why a package is installed.
• npx runs packages without installing them globally.
• process.env.NODE_ENV distinguishes development from production.
• import.meta.url gives the current module’s URL in ES modules.
• node --inspect enables the Chrome DevTools debugger.
• NODE_OPTIONS='--max-old-space-size=4096' increases memory limit.

VS Code

• cmd+shift+p opens the command palette.
• cmd+p opens quick file search.
• cmd+shift+f searches across all files.
• cmd+d selects the next occurrence of current selection.
• cmd+shift+l selects all occurrences of current selection.
• alt+click creates multiple cursors.
• cmd+shift+k deletes the current line.
• alt+up/down moves lines up or down.
• shift+alt+up/down duplicates lines.
• cmd+/ toggles line comments.
• cmd+b toggles the sidebar.
• cmd+j toggles the terminal panel.
• F2 renames a symbol across all references.
• cmd+. shows quick fixes and refactoring options.
• cmd+shift+o navigates to symbols in current file.

Docker

• docker system prune removes unused data.
• docker compose up -d starts services in detached mode.
• docker compose logs -f follows container logs.
• docker exec -it container sh opens a shell in a running container.
• docker cp container:/path ./local copies files from container.
• COPY --chown=node:node sets ownership during build.
• Multi-stage builds dramatically reduce image size.
• .dockerignore works like .gitignore for build context.
• docker stats shows real-time resource usage.
• docker history image shows how an image was built.

General

• Rubber duck debugging actually works - explain the problem out loud.
• Taking a break often solves problems faster than pushing through.
• Writing tests first clarifies what you’re actually trying to build.
• Code is read far more often than it’s written.
• The best code is often the code you delete.
• “Make it work, make it right, make it fast” - in that order.
• Naming is one of the hardest problems in programming.
• If you can’t explain it simply, you don’t understand it well enough.
• Most bugs are caused by incorrect assumptions.
• Version control everything, including configuration.