From 1e410396a491e253e72bbfcf9a529757a02d781e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=99=88=E6=9D=A8=E6=96=87?= <wenermail@gmail.com>
Date: Tue, 27 Sep 2022 22:05:05 +0800
Subject: [PATCH] feat: expose addImportMap (#2429)

---
 docs/api.md                         | 13 +++++++++++++
 docs/import-maps.md                 | 15 +++++++++++++++
 src/features/import-maps.js         |  3 +++
 src/system-node.js                  |  3 +++
 test/browser/dynamic-import-maps.js | 13 +++++++++++++
 test/system-node.mjs                |  2 +-
 6 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/docs/api.md b/docs/api.md
index 319ee8cef..1427cbb93 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -139,3 +139,16 @@ for (const [id, ns] of System.entries()) {
   console.log(ns); // { exportName: 'value' }
 };
 ```
+
+#### System.addImportMap(map [, base])
+Type: `Function`
+
+Allows adding an import map without using the DOM.
+
+```js
+System.addImportMap({
+  "imports": {
+    "y": "/path/to/y.js",
+  }
+})
+```
diff --git a/docs/import-maps.md b/docs/import-maps.md
index 900610586..afbab8daa 100644
--- a/docs/import-maps.md
+++ b/docs/import-maps.md
@@ -200,6 +200,21 @@ Any existing mappings are replaced, although in future this may be an error.
 
 Previous versions of the import maps spec had support for multiple import maps in a single web page ([explanation](https://github.com/WICG/import-maps/issues/199)). SystemJS added support for multiple import maps during that time and has decided to keep support for multiple import maps as an experimental feature ([discussion](https://github.com/systemjs/systemjs/issues/2095)). Note that the Chrome implementation of import maps does not yet allow for multiple maps, and use of multiple import maps within SystemJS should be considered experimental and subject to change.
 
+### Dynamically add Import Maps
+
+> Non-standard Extension
+
+The `addImportMap` method is available to dynamically extend additional mappings into the import map at any time:
+
+```js
+System.addImportMap({
+  "imports": {
+    "y": "/path/to/y.js",
+  }
+})
+```
+
+Any existing map entries will be overridden with the new values.
 ### Handling Import Map Errors
 
 For handling errors when fetching external import maps (specifically for [SystemJS Warning #W4](https://github.com/systemjs/systemjs/blob/master/docs/errors.md#w4)), we can use the `onerror` attribute in the `<script type="systemjs-importmap">` tag.
diff --git a/src/features/import-maps.js b/src/features/import-maps.js
index 9b17315a0..921546927 100644
--- a/src/features/import-maps.js
+++ b/src/features/import-maps.js
@@ -23,6 +23,9 @@ if (hasDocument) {
   processScripts();
   window.addEventListener('DOMContentLoaded', processScripts);
 }
+systemJSPrototype.addImportMap = function (newMap, mapBase) {
+  resolveAndComposeImportMap(newMap, mapBase || baseUrl, importMap);
+}
 
 function processScripts () {
   [].forEach.call(document.querySelectorAll('script'), function (script) {
diff --git a/src/system-node.js b/src/system-node.js
index 42bb15d61..197d69961 100644
--- a/src/system-node.js
+++ b/src/system-node.js
@@ -23,6 +23,9 @@ systemJSPrototype.resolve = function () {
   }
   return originalResolve.apply(this, arguments);
 };
+systemJSPrototype.addImportMap = function (newMap, mapBase){
+  applyImportMap(this, newMap, mapBase)
+}
 
 export function applyImportMap(loader, newMap, mapBase) {
   ensureValidSystemLoader(loader);
diff --git a/test/browser/dynamic-import-maps.js b/test/browser/dynamic-import-maps.js
index 25a04eaa9..c6428781d 100644
--- a/test/browser/dynamic-import-maps.js
+++ b/test/browser/dynamic-import-maps.js
@@ -67,4 +67,17 @@ suite('Dynamic import maps', function () {
       return importAfterImportMap(moduleId);
     });
   });
+
+  test('Loading manually added import map', function () {
+    const moduleId = 'manual-map-1';
+    return importNonExistent(moduleId)
+    .then(function () {
+      System.addImportMap({
+        "imports": {
+          [moduleId]: "./fixtures/browser/esm.js"
+        }
+      })
+      return importAfterImportMap(moduleId);
+    });
+  });
 });
diff --git a/test/system-node.mjs b/test/system-node.mjs
index 2e3f881cf..c30303646 100644
--- a/test/system-node.mjs
+++ b/test/system-node.mjs
@@ -43,7 +43,7 @@ describe('NodeJS version of SystemJS', () => {
     });
 
     it('can load a module from disk without setting base url, before prepareImport is called', async () => {
-      applyImportMap(System, {imports: {"foo": 'file://' + path.join(process.cwd(), 'test/fixtures/register-modules/export.js')}});
+      System.addImportMap({imports: {"foo": 'file://' + path.join(process.cwd(), 'test/fixtures/register-modules/export.js')}});
       const foo = await System.import('foo');
       assert.equal(foo.p, 5);
     });