Allow modules to import files with .json ext.

lib/dependencies.js

@@ -3,6 +3,8 @@
 const fs = require('fs');
 const path = require('path');
 const rawSourceCache = new Map();
+const dependencySuffixes = /\.js|\.mjs|\.json/;
+const dependencySuffixesRight = new RegExp(`(${dependencySuffixes.source})$`);
 
 function escapeModuleSpecifier(string) {
   return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
@@ -25,13 +27,11 @@ function findModuleSpecifiers(source) {
   // be parseable.
   let lines = source.split(/\r?\n/g);
   return lines.reduce((accum, line) => {
-    if (line.includes('.js') || line.includes('.mjs')) {
+    if (dependencySuffixes.test(line)) {
       let parsed = /(import|import\(|from)(\s*)('(.*?)'|"(.*?)")/g.exec(line);
       if (parsed && parsed.length) {
         for (let entry of parsed) {
-          if (entry &&
-              (entry.endsWith('.js') || entry.endsWith('.mjs')) &&
-                !accum.includes(entry)) {
+          if (entry && dependencySuffixesRight.test(entry) && !accum.includes(entry)) {
             accum.push(entry.replace('./', ''));
           }
         }

test/fixtures/fake-test262/test/language/module-code/json-module.js

@@ -0,0 +1,17 @@
+// Copyright (C) 2021 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: This is a test for loading files with a `.json` extension.
+esid: sec-parsemodule
+flags: [module]
+---*/
+
+import './json-module_FIXTURE.json';
+
+/**
+ * At the time of this writing, neither the "import assertions" proposal [1]
+ * nor the "JSON modules" proposal [2] are widely implemented. In order to
+ * verify that the harness correctly identifies JSON dependencies without
+ * requiring the new semantics, this test simply loads a JSON file which
+ * happens to parse as JavaScript, and it does not validate the exported value.
+ */

test/fixtures/fake-test262/test/language/module-code/json-module_FIXTURE.json

@@ -0,0 +1 @@
+"This file is valid JSON and valid JavaScript."