HMR

HMR is an acronym that can refer to several terms depending on the context, with Hot Module Replacement being the most common in software development. Hot Module Replacement describes a development feature in module bundlers and runtimes that updates modules in a running application without performing a full page reload.

In practice, HMR works by detecting changes to source files on a development server, then computing and applying a minimal set of updates to the running application. The intent is to preserve application state and minimize disruption to the running program. In JavaScript ecosystems, HMR relies on a runtime capable of swapping updated modules, re-binding imports, and handling exported values. Depending on the nature of the change, updates may be applied in place, or may require remounting parts of the application; certain changes can still trigger a full reload if hot-swapping is not feasible or safe.

Usage and history: Hot Module Replacement gained prominence with Webpack's development tooling in the mid-2010s and has since been integrated into other builders and frameworks, such as Vite and Parcel. It is valued for speeding the development feedback loop by reducing rebuild and refresh times and by maintaining UI state across edits. Limitations include incompatibilities with some module changes, side-effect-heavy code, or architecture that does not expose hot-swappable boundaries, which can necessitate a full reload or refactor.

Other uses: In different domains, HMR can stand for terms unrelated to software development. The meaning of the acronym is context-dependent and should be clarified within its specific field.