Idempotency

A task runner is a tool that automates repetitive development tasks like compiling code, running tests, minifying assets, and restarting servers. Early web task runners like Grunt and Gulp defined workflows as JavaScript code, while modern approaches use npm scripts, Turborepo, or Nx for monorepo-aware task orchestration. Task runners form the foundation of local development automation, ensuring every team member runs tasks consistently.

Auto-scaling is the ability of a system to automatically adjust the number of running instances or allocated resources based on current demand. When traffic spikes, new instances are provisioned; when demand drops, excess resources are released to save costs. Cloud platforms like AWS, GCP, and Azure offer auto-scaling groups with configurable policies based on CPU usage, request count, queue depth, or custom metrics.

Memoization in React is a performance optimization that caches the result of expensive computations or component renders to avoid redundant work on re-renders. React provides `React.memo()` to skip re-rendering a component when its props haven't changed, `useMemo()` to cache computed values, and `useCallback()` to cache function references. While powerful, premature memoization adds complexity — it's best applied after profiling confirms an actual performance bottleneck.

Hydration is the process where a client-side JavaScript framework attaches event listeners and interactivity to server-rendered HTML markup. After the server sends pre-rendered HTML for fast initial display, the framework "hydrates" it by reconciling its virtual representation with the existing DOM and making it interactive. Hydration can be expensive on complex pages, which has led to innovations like partial hydration, progressive hydration, and React's selective hydration with Suspense.

ETL (Extract, Transform, Load) is an automated data processing pattern where data is extracted from source systems, transformed into a desired format or structure, and loaded into a target system like a data warehouse. Modern variations include ELT, where raw data is loaded first and transformed in place. ETL pipelines are essential for automating data integration, reporting, and feeding clean data into ML training workflows.

Flexbox (Flexible Box Layout) is a one-dimensional CSS layout model designed for distributing space and aligning items within a container along a single axis — either horizontal or vertical. It excels at handling dynamic content sizes, centering elements, and creating flexible navigation bars, card rows, and form layouts. Properties like `justify-content`, `align-items`, and `flex-grow` give you fine-grained control over how items share available space.