Contenthash

Contenthash refers to a hash value that is computed from the actual contents of a file or asset. The key property of a content-based hash is stability: if the content does not change, the hash remains the same, and if the content changes, the hash changes accordingly. This makes contenthashes particularly useful for cache management and long-term caching in deployment pipelines.

In modern asset pipelines, such as those used by Webpack and related tooling, contenthash is commonly used to generate cache-friendly filenames. By including a content-derived hash in the emitted asset’s filename, developers can serve assets with long cache lifetimes while ensuring that updates invalidate only the affected files. Webpack and other tools provide placeholders like [contenthash] in filename templates, for example, [name].[contenthash].js. The hash is typically computed from the asset’s final content, not from the entire build, so unrelated changes do not force a new filename for every asset.

Generation and usage details vary by tool, but the general approach involves applying a cryptographic hash function to the asset’s content after it is produced. Length modifiers, such as [contenthash:8], can be used to shorten the resulting digest. Practically, contenthash works well for static assets (JavaScript, CSS, images) and helps CDNs and browsers cache only what has actually changed.

Caveats include ensuring deterministic content and avoiding non-deterministic metadata that can alter the hash, which could undermine caching benefits. Proper configuration is essential for predictable cache behavior.