feat(tsconfigs): Enable allowJs in base preset (#7274)

.changeset/slimy-hotels-agree.md

@@ -0,0 +1,5 @@
+---
+'astro': minor
+---
+
+Update base `tsconfig.json` template with `allowJs: true` to provide a better relaxed experience for users unfamilliar with TypeScript. `allowJs` is still set to `false` (its default value) when using the `strictest` preset.

packages/astro/tsconfigs/base.json

@@ -25,6 +25,8 @@
     },
     // TypeScript 5.0 changed how `isolatedModules` and `importsNotUsedAsValues` works, deprecating the later
     // Until the majority of users are on TypeScript 5.0, we'll have to supress those deprecation errors
-    "ignoreDeprecations": "5.0"
+    "ignoreDeprecations": "5.0",
+    // Allow JavaScript files to be imported
+    "allowJs": true
   }
 }

packages/astro/tsconfigs/strictest.json

@@ -19,6 +19,8 @@
     // Report an error for unreachable code instead of just a warning.
     "allowUnreachableCode": false,
     // Report an error for unused labels instead of just a warning.
-    "allowUnusedLabels": false
+    "allowUnusedLabels": false,
+    // Disallow JavaScript files from being imported
+    "allowJs": false
   }
 }