Add support for devOptions.hmr (#427)

* Add hmr property to devOptions

* Support for conditionaly using hmr

Only add `import.meta.hot` code during `dev.ts` if it `hmr` devOption is set to `true`.

* Rename hmr variable to isHmr

* Add devOptions.hmr to configuration docs

docs/05-configuration.md

@@ -113,6 +113,8 @@ $ snowpack dev --no-bundle
   - When using the Single-Page Application (SPA) pattern, this is the HTML "shell" file that gets served for every (non-resource) user route. Make sure that you configure your production servers to serve this as well.
 - **`open`** | `string` | Default: `"default"`
   - Opens the dev server in a new browser tab. If Chrome is available on macOS, an attempt will be made to reuse an existing browser tab. Any installed browser may also be specified. E.g., "chrome", "firefox", "brave".
+- **`hmr`** | `boolean` | Default: `true`
+  - Toggles whether or not Snowpack dev server should have HMR enabled.
 
 #### Proxy Options
 

src/commands/dev.ts

@@ -178,7 +178,7 @@ let currentlyRunningCommand: any = null;
 export async function command(commandOptions: CommandOptions) {
   let serverStart = Date.now();
   const {cwd, config} = commandOptions;
-  const {port, open} = config.devOptions;
+  const {port, open, hmr: isHmr} = config.devOptions;
 
   const inMemoryBuildCache = new Map<string, Buffer>();
   const inMemoryResourceCache = new Map<string, string>();
@@ -584,15 +584,15 @@ export async function command(commandOptions: CommandOptions) {
 
       async function wrapResponse(code: string, cssResource: string | undefined) {
         if (isRoute) {
-          code = wrapHtmlResponse(code, true);
+          code = wrapHtmlResponse(code, isHmr);
         } else if (isProxyModule) {
           responseFileExt = '.js';
-          code = wrapEsmProxyResponse(reqPath, code, requestedFileExt, true);
+          code = wrapEsmProxyResponse(reqPath, code, requestedFileExt, isHmr);
         } else if (isCssModule) {
           responseFileExt = '.js';
-          code = await wrapCssModuleResponse(reqPath, code, requestedFileExt, true);
+          code = await wrapCssModuleResponse(reqPath, code, requestedFileExt, isHmr);
         } else if (responseFileExt === '.js') {
-          code = wrapImportMeta(code, {env: true, hmr: true});
+          code = wrapImportMeta(code, {env: true, hmr: isHmr});
         }
         if (responseFileExt === '.js' && cssResource) {
           code = `import './${path.basename(reqPath).replace(/.js$/, '.css.proxy.js')}';\n` + code;

src/config.ts

@@ -97,6 +97,7 @@ export interface SnowpackConfig {
     fallback: string;
     open: string;
     bundle: boolean | undefined;
+    hmr: boolean;
   };
   installOptions: {
     dest: string;
@@ -143,6 +144,7 @@ const DEFAULT_CONFIG: Partial<SnowpackConfig> = {
     open: 'default',
     out: 'build',
     fallback: 'index.html',
+    hmr: true,
     bundle: undefined,
   },
 };
@@ -170,6 +172,7 @@ const configSchema = {
         fallback: {type: 'string'},
         bundle: {type: 'boolean'},
         open: {type: 'string'},
+        hmr: {type: 'boolean'},
       },
     },
     installOptions: {