Memoization

CSS Custom Properties (also called CSS Variables) let you define reusable values with `--my-variable` syntax and reference them anywhere using `var(--my-variable)`. Unlike preprocessor variables in Sass or Less, they are live in the browser, cascade through the DOM, and can be updated dynamically with JavaScript. They're essential for theming systems, dark mode implementations, and maintaining consistent design tokens across large stylesheets.

The View Transitions API is a browser-native way to create animated transitions between different DOM states or page navigations, previously only possible with complex JavaScript animation libraries. It captures a snapshot of the current state, applies the DOM update, then animates between the old and new snapshots using CSS. This API works for both single-page app state changes and multi-page navigations, enabling smooth page transitions with minimal code that feels native to the platform.

Redux is a predictable state management library that stores the entire application state in a single immutable store, updated exclusively through dispatched actions and pure reducer functions. Redux Toolkit (RTK) is now the recommended way to use Redux, dramatically reducing boilerplate with utilities like `createSlice` and `createAsyncThunk`. While Redux remains popular in large enterprise applications that benefit from strict unidirectional data flow and time-travel debugging, lighter alternatives like Zustand have gained ground for simpler use cases.

State management refers to the strategies and tools used to handle, store, and synchronize application data across components in a frontend application. In React, state can live locally in components via `useState`, be shared via Context, or be managed by external libraries like Redux, Zustand, Jotai, or Recoil. Choosing the right state management approach depends on your app's complexity — many apps over-adopt heavy solutions when simpler patterns would suffice.

BEM (Block Element Modifier) is a CSS naming convention that structures class names as `.block__element--modifier` to create clear, predictable relationships between HTML and CSS. For example, `.card__title--highlighted` identifies a highlighted title element within a card block. While modern tooling like CSS Modules and utility frameworks have reduced BEM's necessity, it remains widely used in large codebases and design systems where explicit naming conventions aid team coordination.

CSS Grid is a two-dimensional layout system that lets you define rows and columns simultaneously, making it ideal for complex page layouts. Unlike Flexbox which works in one axis at a time, Grid allows you to place items precisely in both horizontal and vertical directions using named areas or line numbers. Features like `grid-template-areas`, `auto-fill`, and `minmax()` make it possible to create responsive layouts with minimal code.