Which techniques should be applied to reduce JS bundle size?

Short answer: JS bundle size shrinks through a measure-and-prune loop, not a single trick: bundle analysis first, then splitting, shaking, and deferring, and finally a budget that blocks regressions.

Techniques to apply

• Bundle analysis: expose the largest modules; in most projects a handful of libraries carry most of the weight.
• Code splitting: dynamic imports per route and component; code for unseen modals, maps, and charts should not ship in the first load.
• Tree shaking: side-effect-free modules and named imports; fix import patterns that drag in whole libraries.
• Dependency diet: lighter alternatives or built-in APIs instead of heavy libraries; deduplicate repeated versions.
• Deferral: move analytics and marketing scripts to after interaction.
• Modern targets: serve modern builds to current browsers and cut polyfill weight.

For durability, define a size budget in CI so pull requests above the threshold cannot merge. Validate the effect through script evaluation time in Lighthouse and INP plus LCP in field data against your previous baseline.