alternative approach

packages/svelte/src/compiler/phases/1-parse/utils/html.js

@@ -75,8 +75,8 @@ const NUL = 0;
 
 /** @param {number} code */
 function validate_code(code) {
-	// line feed becomes generic whitespace
-	if (code === 10) {
+	// line feed becomes generic whitespace, as does a BOM character
+	if (code === 10 || code === 65279) {
 		return 32;
 	}
 

packages/svelte/src/compiler/utils/sanitize_template_string.js

@@ -1,12 +1,7 @@
-const BOM_CHARACTER = String.fromCharCode(65279);
-
 /**
  * @param {string} str
  * @returns {string}
  */
 export function sanitize_template_string(str) {
-	return str
-		.replace(/(`|\${|\\)/g, '\\$1')
-		.replaceAll(BOM_CHARACTER, '')
-		.replaceAll('', '');
+	return str.replace(/(`|\${|\\)/g, '\\$1');
 }