Avoid installing unused devDependencies at deploy time

package.json

@@ -12,6 +12,7 @@
         "lint-fix": "npx eslint --fix --ext .js,.mjs ./",
         "postinstall": "rm -f .eslintcache && husky",
         "prepare": "husky",
+        "prepare-deploy": "node scripts/prepare-deploy.mjs",
         "size": "size-limit",
         "test": "node --env-file=.env node_modules/@playwright/test/cli test",
         "test:absolute-links": "lychee src/index.html",

scripts/prepare-deploy.mjs

@@ -0,0 +1,67 @@
+/**
+ * @file Running this script before `npm ci` (e.g. in a deployment script) will
+ * remove the `devDependencies` that are not needed in order to deploy. This
+ * way, `npm ci` will install less files and won’t bloat your disk space.
+ *
+ * This is an all-or-nothing script: if a dependency has an invalid name or if
+ * NPM fails at removing one of them, none will be removed. This is because
+ * `npm pkg delete` is called once with all dependencies (fast). This is
+ * way faster than calling it once per dependency.
+ */
+
+import { execSync } from 'node:child_process'
+import console from 'node:console'
+
+console.time('Cleaning of devDependencies list')
+
+/** The list of `devDependencies` not needed to build the app. */
+const USELESS_DEPS = [
+  '@axe-core/playwright',
+  '@eslint/js',
+  '@playwright/test',
+  '@size-limit/preset-app',
+  'axe-html-reporter',
+  'eslint-formatter-codeframe',
+  'eslint-plugin-playwright',
+  'eslint',
+  'globals',
+  'size-limit',
+  'typescript-eslint',
+  'typescript',
+]
+
+const depsArgs = USELESS_DEPS
+  /**
+   * Exclude invalid names, which reduces the risk of failure since we try
+   * to remove all deps in one command: they’ll all be deleted or fail.
+   */
+  .filter(hasValidName)
+
+  // Wrap dep names with single quotes, which is needed for `@scope/name` deps.
+  .map(dep => `'${dep}'`)
+
+  // Create a space-separated list of `devDepencies.'(@scope/)name'`.
+  .join(` devDependencies.`)
+
+try {
+  execSync(`npm pkg delete devDependencies.${depsArgs}`, {
+    stdio: 'inherit',
+    timeout: 5000,
+  })
+} catch (error) {
+  console.warn(`Slicing of devDepencencies failed: ${error.message}`);
+}
+
+console.timeEnd('Cleaning of devDependencies list');
+
+/** Utils */
+
+function hasValidName (name) {
+  const isValid = /^[a-zA-Z0-9@/_.-]+$/.test(name)
+
+  if (!isValid) {
+    console.warn(`Invalid dependency name: ${name} will stay.`)
+  }
+
+  return isValid
+}