refactor: reimplement hmrDownloadManifest in ESM to support more platforms

lib/HotModuleReplacementPlugin.js

@@ -830,7 +830,10 @@ To fix this, make sure to include [runtime] in the output.hotUpdateMainFilename
 											)
 							};
 
-							const source = new RawSource(JSON.stringify(hotUpdateMainJson));
+							const source = new RawSource(
+								(filename.endsWith(".json") ? "" : "export default ") +
+									JSON.stringify(hotUpdateMainJson)
+							);
 							compilation.emitAsset(filename, source, {
 								hotModuleReplacement: true,
 								...assetInfo

lib/config/defaults.js

@@ -1276,7 +1276,11 @@ const applyOutputDefaults = (
 		"hotUpdateChunkFilename",
 		`[id].[fullhash].hot-update.${output.module ? "mjs" : "js"}`
 	);
-	D(output, "hotUpdateMainFilename", "[runtime].[fullhash].hot-update.json");
+	D(
+		output,
+		"hotUpdateMainFilename",
+		`[runtime].[fullhash].hot-update.${output.module ? "json.mjs" : "json"}`
+	);
 	D(output, "crossOriginLoading", false);
 	F(output, "scriptType", () => (output.module ? "module" : false));
 	D(

lib/esm/ModuleChunkLoadingRuntimeModule.js

@@ -424,13 +424,10 @@ class ModuleChunkLoadingRuntimeModule extends RuntimeModule {
 						`${
 							RuntimeGlobals.hmrDownloadManifest
 						} = ${runtimeTemplate.basicFunction("", [
-							'if (typeof fetch === "undefined") throw new Error("No browser support: need fetch API");',
+							`return ${importFunctionName}(/* webpackIgnore: true */ ${RuntimeGlobals.publicPath} + ${
-							`return fetch(${RuntimeGlobals.publicPath} + ${
 								RuntimeGlobals.getUpdateManifestFilename
-							}()).then(${runtimeTemplate.basicFunction("response", [
+							}()).then(${runtimeTemplate.basicFunction("obj", [
-								"if(response.status === 404) return; // no update available",
+								"return obj.default;"
-								'if(!response.ok) throw new Error("Failed to fetch update manifest " + response.statusText);',
-								"return response.json();"
 							])});`
 						])};`
 					])

test/Defaults.unittest.js

@@ -968,6 +968,9 @@ describe("snapshots", () => {
 		-     "hotUpdateChunkFilename": "[id].[fullhash].hot-update.js",
 		+     "hotUpdateChunkFilename": "[id].[fullhash].hot-update.mjs",
 		@@ ... @@
+		-     "hotUpdateMainFilename": "[runtime].[fullhash].hot-update.json",
+		+     "hotUpdateMainFilename": "[runtime].[fullhash].hot-update.json.mjs",
+		@@ ... @@
 		-     "iife": true,
 		+     "iife": false,
 		@@ ... @@