JavaScript Performance Optimization: Techniques That Actually Move Metrics
Most optimization advice is folklore. Here are the techniques that measurably improved my applications. Performance optimization in JavaScript is full of folk wisdom that does not survive measurement. The techniques that actually move my metrics are unglamorous: reduce work, defer work, and move work off the main thread. I approach optimization as a measurement-driven process where every change is verified against a baseline, because unmeasured optimization is just refactoring with extra confidence. Measure Before Optimizing Before changing anything, I establish a baseline using the Performance panel or a custom performance.now timing around the critical path. Optimization without a baseline is guessing, and I have wasted days on changes that felt faster but were noise. The baseline also tells me whether the function I am tempted to optimize is even a significant fraction of the total time. If it is five percent of the budget, even halving it barely moves the metric. Reduce Algorithmic Complexity First The biggest wins come from algorithmic changes, not micro-optimizations. Replacing a nested loop with a hash lookup turns an O(n squared) operation into O(n), which can be a thousand-fold…