From 8468e8a0d1591138b32b16c68c293868b4b4f361 Mon Sep 17 00:00:00 2001
From: Klaus Reimer <k@ailis.de>
Date: Tue, 3 Jun 2025 23:35:27 +0200
Subject: [PATCH 1/2] Implement support for a JSON configuration file

---
 README.md   | 18 ++++++++++++++++++
 src/cli.mjs | 21 +++++++++++++++------
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index d32e764..ae670de 100644
--- a/README.md
+++ b/README.md
@@ -55,6 +55,24 @@ The CLI supports the following options:
 - `--entrypoint <file>`: Confirm the specified file and its transitive dependencies can be resolved using the generated import map. Auto-enabled when importmap is written into an HTML file. Can be specified multiple times.
 - `--dev`: Include devDependencies from `package.json`. Also favor `"development"` in [package exports](https://nodejs.org/docs/latest-v16.x/api/packages.html#packages_conditions_definitions)</a><sup>↗</sup>.
 - `--keep-unused`: Keep all mappings, even if they are not currently used by entry file or its transitive dependencies.
+- `--config <file>`: Read additional settings from the given JSON configuration file.
+
+#### Configuration file
+
+A configuration file in JSON format can be specified with the `--config` CLI option. The following example shows such a JSON file with all supported properties set to their default values:
+
+```json
+{
+  "dir": ".",
+  "dev": false,
+  "keepUnused": false,
+  "entryPoints": [],
+  "manualImportmap": {},
+  "packagesManualOverrides": {}
+}
+```
+
+All properties are optional and CLI options like `--dev`, `--entrypoint` and `--keep-unused` will override the values read from the config. The objects `manualImportmap` and `packagesManualOverrides` have the same format as the corresponding objects in the API.
 
 ### API
 
diff --git a/src/cli.mjs b/src/cli.mjs
index 5f2189b..187e3ce 100755
--- a/src/cli.mjs
+++ b/src/cli.mjs
@@ -1,5 +1,6 @@
 #!/usr/bin/env node
 
+import { readFile } from "node:fs/promises";
 import { pathToFileURL } from "node:url";
 import { parseArgs } from "node:util";
 import { writeImportmaps } from "./main.js";
@@ -21,10 +22,12 @@ const options = {
   "keep-unused": {
     type: "boolean",
   },
+  "config": {
+    type: "string",
+  },
 };
 const { values, positionals } = parseArgs({ options, allowPositionals: true });
 const outfile = positionals[0];
-values.entrypoint ??= [];
 
 if (values.help || positionals.length === 0) {
   usage();
@@ -46,21 +49,26 @@ if (
   process.exit(1);
 }
 
+const config = values.config ? JSON.parse(await readFile(values.config)) : {};
+const dev = values.dev ?? config.dev;
+
 const currentDirectoryUrl = pathToFileURL(`${process.cwd()}/`);
 await writeImportmaps({
-  directoryUrl: new URL(values.dir || ".", currentDirectoryUrl),
+  directoryUrl: new URL(values.dir ?? config.dir ?? ".", currentDirectoryUrl),
   importmaps: {
     [outfile]: {
       nodeMappings: {
-        devDependencies: values.dev,
-        packageUserConditions: values.dev ? ["development"] : [],
+        devDependencies: dev,
+        packageUserConditions: dev ? ["development"] : [],
       },
       importResolution: {
-        entryPoints: values.entryPoints,
+        entryPoints: values.entrypoint ?? config.entryPoints ?? [],
       },
-      keepUnusedMappings: values["keep-unused"],
+      keepUnusedMappings: values["keep-unused"] ?? config.keepUnused,
+      manualImportmap: config.manualImportmap,
     },
   },
+  packagesManualOverrides: config.packagesManualOverrides,
 });
 
 function usage() {
@@ -76,6 +84,7 @@ Options:
   --entrypoint file.js Confirm the specified file and its transitive dependencies can be resolved using the generated import map. Can be specified multiple times.
   --dev                Include devDependencies from package.json and pick "developement" in package conditions.
   --keep-unused        Remove mappings not used by any entrypoint or their transitive dependencies. Requires --entrypoint.
+  --config config.json Read additional settings from the given JSON configuration file.
 
 For more advanced options, see the API.`);
 }

From 29a7de11cd706a4ac405da4db97f74d89f2b585c Mon Sep 17 00:00:00 2001
From: Klaus Reimer <k@ailis.de>
Date: Tue, 3 Jun 2025 23:41:25 +0200
Subject: [PATCH 2/2] Add missing encoding parameter

---
 src/cli.mjs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/cli.mjs b/src/cli.mjs
index 187e3ce..1ace50b 100755
--- a/src/cli.mjs
+++ b/src/cli.mjs
@@ -49,7 +49,7 @@ if (
   process.exit(1);
 }
 
-const config = values.config ? JSON.parse(await readFile(values.config)) : {};
+const config = values.config ? JSON.parse(await readFile(values.config, "utf-8")) : {};
 const dev = values.dev ?? config.dev;
 
 const currentDirectoryUrl = pathToFileURL(`${process.cwd()}/`);