TypeScript

usePrevious — Track Last Render's Value

Returns the value the prop/state had on the previous render. Useful for detecting transitions (e.g. "the count just went from 0 to 1") inside effects.

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Kotlin

Parameterized Tests with JUnit 5

JUnit 5 + Kotlin: `@ParameterizedTest` runs the same test body with multiple input rows. `@CsvSource` for inline data, `@MethodSource` for complex args.

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Go

Variadic Functions

`...T` in the last parameter slot accepts zero or more T values. Pass a slice by suffixing with `...` to spread it. Used everywhere from `fmt.Println` to custom builders.

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Go

log/slog — Structured Logging

`log/slog` (Go 1.21+) is the standard structured logger. Drop-in replacement for `log` with key/value attributes and JSON output for log-pipeline ingestion.

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Python

Multipart File Upload

POST a file (or several) as multipart/form-data using requests, with optional extra form fields. Lets you upload to /avatar-style endpoints without manual boundary construction.

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PHP

Simple cURL GET with Timeout

A no-dependency HTTP GET helper with sensible defaults: short timeout, follow redirects, return body as string, throw on transport error. Pass extra headers as a simple associative array.

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Bash

Run Command with Timeout

`timeout` (GNU coreutils) kills a command after N seconds. Returns exit code 124 on timeout — let the caller distinguish "timed out" from "failed for other reasons."

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Bash

Check Command Exists Before Using It

`command -v` is the portable, fast way to check whether a binary is on $PATH. Avoid `which` (its behavior varies between systems).

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HTML

Multi-Column Footer

Standard site footer with grouped links, brand block, social icons, and legal/copyright. Use semantic `<nav aria-label>` on each column so screen readers announce the section labels.

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Rust

Arc<Mutex<T>> — Shared Mutable State

Share mutable data across threads: `Arc` for the shared ownership, `Mutex` for the synchronized access. Lock with `.lock().unwrap()`; the guard drops the lock on scope exit.

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TypeScript

Environment Variable Validator

Validate process.env at boot-time and exit fast if anything's missing. The returned object is typed so the rest of the code reads `env.DATABASE_URL` instead of `process.env.DATABASE_URL!`.

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SQL

UPSERT — PostgreSQL ON CONFLICT

`INSERT ... ON CONFLICT DO UPDATE` inserts a row, or updates the existing one if a unique-constraint collision happens. The atomic alternative to "SELECT, then INSERT or UPDATE".

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Java

Generic Class with Type Parameter

Stamp out type-safe containers and helpers — same class body, multiple element types. The `<T>` declaration is what makes it generic.

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Rust

Read a File — Whole / Lines / Bytes

Three common patterns: load it all into memory, iterate line-by-line, or stream bytes. Pick by file size — `read_to_string` is convenient but bad for huge files.

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SQL

Median with PERCENTILE_CONT

SQL has no `MEDIAN()` — use `PERCENTILE_CONT(0.5) WITHIN GROUP`. The same function gets you P95, P99, quartiles, etc. for latency analysis.

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Python

logging.basicConfig with Rotating File

A solid logging setup: rich format, rotating file handler so logs don't fill the disk, plus a console handler at a higher level so noisy DEBUG only goes to the file.

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Kotlin

with — Scope an Existing Object

`with(x) { ... }` is `run` flipped: the receiver is the first argument. Reads naturally when you're doing several things to an existing object without chaining.

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Bash

Parse --flag=value Arguments

A getopts-free arg parser handling long flags, equals-separated values, and bundled short flags. Customize as needed.

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Rust

Async/Await with tokio

`async fn` returns a future; `.await` drives it. tokio is the de-facto runtime. The `#[tokio::main]` attribute turns `main` into the runtime entry point.

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Python

asyncio.to_thread — Run Blocking Code

Wrap a blocking function so it doesn't freeze the event loop. asyncio.to_thread (3.9+) schedules the call onto the default executor and awaits the result.

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HTML

Tabs (ARIA tablist pattern)

The accessible tab pattern: a `role="tablist"` container, each tab as `role="tab"`, panels as `role="tabpanel"`. `aria-selected` + `aria-controls` link them and announce state.

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PHP

Tail Last N Lines of File

Efficiently read the last N lines of a (possibly large) file by seeking to the end and walking backwards in fixed-size chunks. Avoids loading the entire file into memory.

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Go

Empty Struct Sentinel (struct{})

`struct{}` is a zero-size value — no memory cost. Use it as the value type in a Set (`map[T]struct{}`), as a channel signal (`chan struct{}`), or as a marker type.

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SQL

Self-Join — Org Chart / Hierarchies

A self-join is just a regular join with the same table aliased twice. The canonical example is an employee table where each row points to a manager in the same table.

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Go

Multiple Return Values + Named Returns

Go functions can return multiple values — most idiomatically a `(result, error)` pair. Named returns let you document the meaning of each value AND enable naked returns in short functions.

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Bash

Extract JSON Field with jq

jq is the de-facto JSON tool. Pipe any JSON in, get a parsed/filtered/reshaped result out. Indispensable in deploy scripts that consume API output.

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Rust

Group By a Key (fold into HashMap)

No built-in `group_by`, but `fold` into a `HashMap` does the same thing in two lines — and the type system tracks keys / values correctly.

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HTML

Main Content + Aside Sidebar

`<main>` wraps the unique-to-this-page content (screen readers jump to it with a keyboard shortcut). `<aside>` is supporting / tangential content — sidebars, callouts, related links.

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Bash

Run on Multiple Hosts via SSH (with progress)

Iterate a host list, run the same command on each, show colored OK/FAIL summary at the end. Useful for ad-hoc fleet operations without setting up Ansible.

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HTML

Audio Element

`<audio>` is video's simpler sibling. Use it for podcasts, music samples, sound effects on play. Same multi-`<source>` pattern for cross-browser format support.

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