# CSS Optimization: Is UDJO Still Effective Today? Evaluating the relevance of the Don't Repeat Yourself principle in modern CSS workflows. - **Source:** [CSS-Tricks (feeds.feedburner.com)](https://css-tricks.com) - **Published:** 2026-11-10 - **Topic:** [technology](https://brifing.si/c/technology) - **Original article:** - **On Brifing:** https://brifing.si/s/5c3d772a-c554-4a91-b8ce-2cfd3b07872c ## The UDJO Concept The Using Declarations Just Once strategy draws inspiration from the DRY principle, aiming to eliminate CSS repetition. By identifying redundant style properties across a stylesheet, developers attempt to consolidate declarations into single, reusable units. This approach seeks to minimize file size and improve maintainability within complex, large-scale web application codebases. ## Historical Context Historically, UDJO was a popular optimization technique when bandwidth was severely limited and CSS files were manually managed. Developers prioritized reducing the total byte count of stylesheets to ensure faster initial page loads. This manual consolidation was essential before the advent of modern build tools and automated CSS minification processes. ## Modern Build Tools Today, automated build pipelines handle CSS optimization through minification and tree-shaking processes. These tools automatically strip whitespace, shorten identifiers, and merge redundant rules without manual developer intervention. Consequently, the manual effort required to implement UDJO often yields diminishing returns compared to the efficiency provided by contemporary automated development workflows. ## Performance Implications Modern browser engines are highly optimized for parsing CSS, making minor declaration repetitions negligible for overall rendering performance. While reducing file size remains beneficial for mobile users on slow networks, the overhead of complex class naming structures required for UDJO can sometimes complicate the DOM and increase overall maintenance costs. ## Maintainability Trade-offs Strict adherence to UDJO can lead to overly abstract CSS architectures that are difficult for new developers to navigate. When styles are decoupled from their components to satisfy a single-declaration rule, the cognitive load increases significantly. Balancing optimization with code readability is a critical challenge for modern frontend engineering teams today. ## CSS Variables Impact The introduction of native CSS custom properties has fundamentally changed how developers approach repetition. Instead of forcing a single declaration, developers now define variables for repeated values like colors or spacing. This provides a more flexible and readable way to maintain consistency across a project without sacrificing the semantic clarity of components. ## Component-Based Architectures Modern frameworks like React or Vue encourage component-based styling, where CSS is often scoped to specific UI elements. This paradigm shift prioritizes encapsulation over global declaration reuse. While UDJO focuses on global efficiency, component-based styles prioritize modularity, making the two approaches fundamentally different in their application and long-term project impact. ## Strategic Conclusion While the core intent of UDJO remains valid, its manual application is largely outdated in modern development environments. Developers should focus on leveraging CSS variables and automated build tools rather than obsessing over single-declaration reuse. Prioritizing maintainable, scalable code structures is more effective than chasing minor byte-level optimizations in today's landscape. ## Sources covering this story - https://css-tricks.com/css-using-declarations-just-once/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._