persist-previous-build-assets copies previous build artifacts into the latest deployment so users with older HTML do not hit missing hashed JavaScript or CSS chunks.

It targets a practical production failure mode: a new deploy ships, old chunk URLs disappear, and active users see chunk-loading errors.

Why it matters

Reliability work is often small glue code around the edges of deployment. Preserving previous assets gives frontend applications a safer deploy path without requiring a larger infrastructure rewrite.

Full documentation, synced from the package README:

Fix for "missing chunks" webpack issue where clients are outdated and chunks are 404ing.

These 404s result in "SyntaxError Unexpected token '<'", "Loading chunk 14 failed." etc.

TLDR; this package downloads previous manifest assets & adds them to your build dir

Why

When a new hashed deploymend goes out to hosting providers like Netlify, the previous hashed JS/CSS files aren't included in that "live site". This means if a user is on your site while you do a deployment, they could encounter 404 errors from stale webpack files no longer existing.

This package makes certain the previous build artifacts are added to the latest deployment.

Install

npm install persist-previous-build-assets -D

Usage

Add to a pre or post build script

{
  "name": "your-pkg-json",
  "scripts": {
    "build": "react-scripts build",
    "postbuild": "node ./persist-previous-assets.js",
  },
}

This will run the below code when npm run build is executed before build is done.

// persist-previous-assets.js
const path = require('path')
const persistPreviousBuildAssets = require('persist-previous-build-assets')

persistPreviousBuildAssets({
  manifestUrl: 'https://site.com/asset-manifest.json',
  outputDir: path.resolve(__dirname, 'build')
}).then(() => {
  console.log('Done!')
})

Other Solutions

See this article for additional ways to address this problem

Links

• Package source
• npm package