disable preload during preview (#599)

Author: mbostock

bin/observable.ts

@@ -1,6 +1,7 @@
 import {type ParseArgsConfig, parseArgs} from "node:util";
 import {readConfig} from "../src/config.js";
 import {CliError} from "../src/error.js";
+import {enableNpmVersionResolution, enableRemoteModulePreload} from "../src/javascript/imports.js";
 import {red} from "../src/tty.js";
 
 const args = process.argv.slice(2);
@@ -129,6 +130,8 @@ try {
           }
         }
       });
+      enableNpmVersionResolution(false);
+      enableRemoteModulePreload(false);
       await import("../src/preview.js").then(async (preview) =>
         preview.preview({
           config: await readConfig(config, root),

src/javascript/imports.ts

@@ -15,6 +15,17 @@ import {getFeature, getFeatureReferenceMap, getStringLiteralValue, isStringLiter
 type ImportNode = ImportDeclaration | ImportExpression;
 type ExportNode = ExportAllDeclaration | ExportNamedDeclaration;
 
+let npmVersionResolutionEnabled = true;
+let remoteModulePreloadEnabled = true;
+
+export function enableNpmVersionResolution(enabled = true) {
+  npmVersionResolutionEnabled = enabled;
+}
+
+export function enableRemoteModulePreload(enabled = true) {
+  remoteModulePreloadEnabled = enabled;
+}
+
 export interface ImportsAndFeatures {
   imports: ImportReference[];
   features: Feature[];
@@ -305,6 +316,7 @@ function formatNpmSpecifier({name, range, path}: {name: string; range?: string;
 const fetchCache = new Map<string, Promise<{headers: Headers; body: any}>>();
 
 async function cachedFetch(href: string): Promise<{headers: Headers; body: any}> {
+  if (!remoteModulePreloadEnabled) throw new Error("remote module preload is not enabled");
   let promise = fetchCache.get(href);
   if (promise) return promise;
   promise = (async () => {
@@ -320,6 +332,7 @@ async function cachedFetch(href: string): Promise<{headers: Headers; body: any}>
 }
 
 async function resolveNpmVersion(specifier: string): Promise<string> {
+  if (!npmVersionResolutionEnabled) throw new Error("npm version resolution is not enabled");
   const {name, range} = parseNpmSpecifier(specifier); // ignore path
   specifier = formatNpmSpecifier({name, range});
   const search = range ? `?specifier=${range}` : "";
@@ -396,6 +409,7 @@ const integrityCache = new Map<string, string>();
  * precomputes the subresource integrity hash for each fetched module.
  */
 export async function resolveModulePreloads(hrefs: Set<string>): Promise<void> {
+  if (!remoteModulePreloadEnabled) return;
   let resolve: () => void;
   const visited = new Set<string>();
   const queue = new Set<Promise<void>>();