diff --git a/packages/svelte/src/compiler/index.js b/packages/svelte/src/compiler/index.js
index 599206ac6a..f637179597 100644
--- a/packages/svelte/src/compiler/index.js
+++ b/packages/svelte/src/compiler/index.js
@@ -4,7 +4,6 @@
 import { walk as zimmerframe_walk } from 'zimmerframe';
 import { convert } from './legacy.js';
 import { parse as _parse, Parser } from './phases/1-parse/index.js';
-import { remove_typescript_nodes } from './phases/1-parse/remove_typescript_nodes.js';
 import { parse_stylesheet } from './phases/1-parse/read/style.js';
 import { analyze_component, analyze_module } from './phases/2-analyze/index.js';
 import { transform_component, transform_module } from './phases/3-transform/index.js';
@@ -26,7 +25,7 @@ export function compile(source, options) {
 
 	const validated = validate_component_options(options, '');
 
-	let parsed = _parse(source);
+	const parsed = _parse(source, false, true);
 
 	const { customElement: customElementOptions, ...parsed_options } = parsed.options || {};
 
@@ -39,20 +38,6 @@ export function compile(source, options) {
 		runes: 'runes' in parsed_options ? () => parsed_options.runes : validated.runes
 	};
 
-	if (parsed.metadata.ts) {
-		parsed = {
-			...parsed,
-			fragment: parsed.fragment && remove_typescript_nodes(parsed.fragment),
-			instance: parsed.instance && remove_typescript_nodes(parsed.instance),
-			module: parsed.module && remove_typescript_nodes(parsed.module)
-		};
-		if (combined_options.customElementOptions?.extend) {
-			combined_options.customElementOptions.extend = remove_typescript_nodes(
-				combined_options.customElementOptions?.extend
-			);
-		}
-	}
-
 	const analysis = analyze_component(parsed, source, combined_options);
 	const result = transform_component(analysis, source, combined_options);
 	result.ast = to_public_ast(source, parsed, options.modernAst);
diff --git a/packages/svelte/src/compiler/phases/1-parse/index.js b/packages/svelte/src/compiler/phases/1-parse/index.js
index 3fb7243e39..fa3c2ff808 100644
--- a/packages/svelte/src/compiler/phases/1-parse/index.js
+++ b/packages/svelte/src/compiler/phases/1-parse/index.js
@@ -73,8 +73,9 @@ export class Parser {
 	/**
 	 * @param {string} template
 	 * @param {boolean} loose
+	 * @param {boolean} [erase] hand back JavaScript for TypeScript input, as the compiler wants it
 	 */
-	constructor(template, loose) {
+	constructor(template, loose, erase = false) {
 		if (typeof template !== 'string') {
 			throw new TypeError('Template must be a string');
 		}
@@ -92,9 +93,11 @@ export class Parser {
 		this.ts = match_lang?.[2] === 'ts';
 		this.js = new Source(this.template, {
 			sourceType: 'module',
-			typescript: this.ts,
+			typescript: this.ts && (erase ? 'erase' : true),
 			comments: true,
-			locations: true
+			locations: true,
+			// a script may export what the component declares elsewhere
+			allowUndeclaredExports: true
 		});
 
 		this.root = {
@@ -337,12 +340,13 @@ export class Parser {
 /**
  * @param {string} template
  * @param {boolean} [loose]
+ * @param {boolean} [erase] hand back JavaScript for TypeScript input, as the compiler wants it
  * @returns {AST.Root}
  */
-export function parse(template, loose = false) {
+export function parse(template, loose = false, erase = false) {
 	state.set_source(template);
 
-	const parser = new Parser(template, loose);
+	const parser = new Parser(template, loose, erase);
 	return parser.root;
 }
 
diff --git a/packages/svelte/src/compiler/phases/1-parse/js.js b/packages/svelte/src/compiler/phases/1-parse/js.js
index af965e259d..6a60d01af7 100644
--- a/packages/svelte/src/compiler/phases/1-parse/js.js
+++ b/packages/svelte/src/compiler/phases/1-parse/js.js
@@ -5,45 +5,73 @@ import * as teasel from '@teasel/parser';
 import * as e from '../../errors.js';
 
 /**
+ * A standalone module, as `analyze_module` reads one.
  * @param {string} source
  * @param {AST.JSComment[]} comments
  * @param {boolean} typescript
- * @param {boolean} [is_script] a `<script>` may export names the component declares elsewhere
  * @returns {Program}
  */
-export function parse(source, comments, typescript, is_script) {
+export function parse(source, comments, typescript) {
+	let ast;
 	try {
-		const ast = teasel.parse(source, {
+		ast = teasel.parse(source, {
 			sourceType: 'module',
 			typescript,
 			comments: true,
-			locations: true,
-			allowUndeclaredExports: is_script
+			locations: true
 		});
+	} catch (err) {
+		return handle_parse_error(err);
+	}
 
-		add_comments(source, comments, /** @type {teasel.Comment[]} */ (ast.comments));
-		delete ast.comments;
+	add_comments(source, comments, /** @type {teasel.Comment[]} */ (ast.comments));
+	delete ast.comments;
 
-		return ast;
+	return ast;
+}
+
+/**
+ * The program inside a `<script>`, with the positions of the whole template.
+ * @param {Parser} parser
+ * @param {number} start
+ * @param {number} end
+ * @returns {Program}
+ */
+export function parse_script(parser, start, end) {
+	let ast;
+	try {
+		ast = parser.js.parse(start, end);
 	} catch (err) {
 		return handle_parse_error(err);
 	}
+
+	add_comments(
+		parser.template,
+		parser.root.comments,
+		/** @type {teasel.Comment[]} */ (ast.comments)
+	);
+	delete ast.comments;
+	unsupported(ast.typescript);
+	delete ast.typescript;
+
+	return ast;
 }
 
 /**
  * @param {Parser} parser
  * @param {number} index
- * @param {'as' | 'in'} [until] a word operator the expression stops before, at the top level
+ * @param {'as'} [until] the host's `as` follows the expression, as an each block's item does
  * @returns {{ node: Expression, end: number }}
  */
 export function parse_expression_at(parser, index, until) {
+	let answer;
 	try {
-		const { node, end, comments } = parser.js.parseExpressionAt(index, until);
-		add_comments(parser.template, parser.root.comments, /** @type {teasel.Comment[]} */ (comments));
-		return { node, end };
+		answer = parser.js.parseExpressionAt(index, until);
 	} catch (err) {
 		return handle_parse_error(err);
 	}
+
+	return accept(parser, answer, answer.node);
 }
 
 /**
@@ -52,29 +80,30 @@ export function parse_expression_at(parser, index, until) {
  * @returns {{ node: Pattern, end: number }}
  */
 export function parse_pattern_at(parser, index) {
+	let answer;
 	try {
-		const { node, end, comments } = parser.js.parsePatternAt(index);
-		add_comments(parser.template, parser.root.comments, /** @type {teasel.Comment[]} */ (comments));
-		return { node, end };
+		answer = parser.js.parsePatternAt(index);
 	} catch (err) {
 		return handle_parse_error(err);
 	}
+
+	return accept(parser, answer, answer.node);
 }
 
 /**
  * @param {Parser} parser
- * @param {string} source
  * @param {number} index the opening paren
- * @returns {{ params: Pattern[], end: number }}
+ * @returns {{ node: Pattern[], end: number }}
  */
 export function parse_params_at(parser, index) {
+	let answer;
 	try {
-		const { params, end, comments } = parser.js.parseParamsAt(index);
-		add_comments(parser.template, parser.root.comments, /** @type {teasel.Comment[]} */ (comments));
-		return { params, end };
+		answer = parser.js.parseParamsAt(index);
 	} catch (err) {
 		return handle_parse_error(err);
 	}
+
+	return accept(parser, answer, answer.params);
 }
 
 /**
@@ -83,10 +112,9 @@ export function parse_params_at(parser, index) {
  * @returns {{ node: Statement, end: number }}
  */
 export function parse_statement_at(parser, index) {
+	let answer;
 	try {
-		const { node, end, comments } = parser.js.parseStatementAt(index);
-		add_comments(parser.template, parser.root.comments, /** @type {teasel.Comment[]} */ (comments));
-		return { node, end };
+		answer = parser.js.parseStatementAt(index);
 	} catch (err) {
 		// A statement that runs to the end of the source (e.g. an unterminated declaration tag)
 		// is an EOF, not a stray token; preserve the friendlier `unexpected_eof` diagnostic.
@@ -94,6 +122,48 @@ export function parse_statement_at(parser, index) {
 			e.unexpected_eof(parser.template.length);
 		return handle_parse_error(err);
 	}
+
+	return accept(parser, answer, answer.node);
+}
+
+/**
+ * Keeps an answer's comments, rejects what erasure could not express, and hands back the node
+ * with the offset the parse stopped at.
+ * @template T
+ * @param {Parser} parser
+ * @param {{ end: number, comments?: teasel.Comment[], typescript?: teasel.Kept[] }} answer
+ * @param {T} node
+ * @returns {{ node: T, end: number }}
+ */
+function accept(parser, answer, node) {
+	add_comments(
+		parser.template,
+		parser.root.comments,
+		/** @type {teasel.Comment[]} */ (answer.comments)
+	);
+	unsupported(answer.typescript);
+	return { node, end: answer.end };
+}
+
+/** What erasure leaves in place needs a compiler, not this one */
+const UNSUPPORTED = {
+	TSEnumDeclaration: 'enums',
+	TSModuleDeclaration: 'namespaces with non-type nodes',
+	TSParameterProperty: 'accessibility modifiers on constructor parameters',
+	Decorator: 'decorators (related TSC proposal is not stage 4 yet)',
+	TSExportAssignment: 'export assignments',
+	TSImportEqualsDeclaration: 'import assignments'
+};
+
+/** @param {teasel.Kept[] | undefined} kept */
+function unsupported(kept) {
+	const node = kept?.[0];
+	if (node) {
+		e.typescript_invalid_feature(
+			node,
+			UNSUPPORTED[/** @type {keyof typeof UNSUPPORTED} */ (node.type)] ?? node.type
+		);
+	}
 }
 
 const regex_position_indicator = / \(\d+:\d+\)$/;
diff --git a/packages/svelte/src/compiler/phases/1-parse/read/expression.js b/packages/svelte/src/compiler/phases/1-parse/read/expression.js
index 5a0a30e5ac..1f8a051f47 100644
--- a/packages/svelte/src/compiler/phases/1-parse/read/expression.js
+++ b/packages/svelte/src/compiler/phases/1-parse/read/expression.js
@@ -33,7 +33,7 @@ export function get_loose_identifier(parser, opening_token) {
  * @param {Parser} parser
  * @param {string} [opening_token]
  * @param {boolean} [disallow_loose]
- * @param {'as' | 'in'} [until] a word operator the expression stops before, at the top level
+ * @param {'as'} [until] the host's `as` follows the expression, as an each block's item does
  * @returns {Expression}
  */
 export default function read_expression(parser, opening_token, disallow_loose, until) {
diff --git a/packages/svelte/src/compiler/phases/1-parse/read/script.js b/packages/svelte/src/compiler/phases/1-parse/read/script.js
index b81c0c68b2..2b36d11fd4 100644
--- a/packages/svelte/src/compiler/phases/1-parse/read/script.js
+++ b/packages/svelte/src/compiler/phases/1-parse/read/script.js
@@ -1,8 +1,7 @@
 /** @import { Program } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { Parser } from '../index.js' */
-import { parse } from '../js.js';
-import { regex_not_newline_characters } from '../../patterns.js';
+import { parse_script } from '../js.js';
 import * as e from '../../../errors.js';
 import * as w from '../../../warnings.js';
 import { is_text_attribute } from '../../../utils/ast.js';
@@ -22,19 +21,14 @@ const ALLOWED_ATTRIBUTES = ['context', 'generics', 'lang', 'module'];
  */
 export function read_script(parser, start, attributes) {
 	const script_start = parser.index;
-	const data = parser.read_until_regex(regex_closing_script_tag);
+	parser.read_until_regex(regex_closing_script_tag);
 	if (parser.index >= parser.template.length) {
 		e.element_unclosed(parser.template.length, 'script');
 	}
 
-	const source =
-		parser.template.slice(0, script_start).replace(regex_not_newline_characters, ' ') + data;
+	const ast = parse_script(parser, script_start, parser.index);
 	parser.read(regex_starts_with_closing_script_tag);
 
-	const ast = parse(source, parser.root.comments, parser.ts, true);
-
-	ast.start = script_start;
-
 	if (ast.loc) {
 		// Acorn always uses `0` as the start of a `Program`, but for sourcemap purposes
 		// we need it to be the start of the `<script>` contents
diff --git a/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js b/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
deleted file mode 100644
index f573147367..0000000000
--- a/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
+++ /dev/null
@@ -1,188 +0,0 @@
-/** @import { Context, Visitors } from 'zimmerframe' */
-/** @import { FunctionExpression, FunctionDeclaration } from 'estree' */
-import { walk } from 'zimmerframe';
-import * as b from '#compiler/builders';
-import * as e from '../../errors.js';
-
-/**
- * @param {FunctionExpression | FunctionDeclaration} node
- * @param {Context<any, any>} context
- */
-function remove_this_param(node, context) {
-	if (node.params[0]?.type === 'Identifier' && node.params[0].name === 'this') {
-		node.params.shift();
-	}
-	return context.next();
-}
-
-/** @type {Visitors<any, null>} */
-const visitors = {
-	_(node, context) {
-		const n = context.next() ?? node;
-
-		// TODO there may come a time when we decide to preserve type annotations.
-		// until that day comes, we just delete them so they don't confuse esrap
-		delete n.typeAnnotation;
-		delete n.typeParameters;
-		delete n.typeArguments;
-		delete n.returnType;
-		delete n.accessibility;
-		delete n.readonly;
-		delete n.definite;
-		delete n.override;
-
-		// `optional` is reused by JS optional chaining (`a?.b`, `a?.()`), so only
-		// strip the TypeScript optional marker (`x?: T`, `m?(): T`, `x?: T` fields)
-		if (n.type !== 'MemberExpression' && n.type !== 'CallExpression') {
-			delete n.optional;
-		}
-	},
-	Decorator(node) {
-		e.typescript_invalid_feature(node, 'decorators (related TSC proposal is not stage 4 yet)');
-	},
-	ImportDeclaration(node) {
-		if (node.importKind === 'type') return b.empty;
-
-		if (node.specifiers?.length > 0) {
-			const specifiers = node.specifiers.filter((/** @type {any} */ s) => s.importKind !== 'type');
-			if (specifiers.length === 0) return b.empty;
-
-			return { ...node, specifiers };
-		}
-
-		return node;
-	},
-	ExportNamedDeclaration(node, context) {
-		if (node.exportKind === 'type') return b.empty;
-
-		if (node.declaration) {
-			const result = context.next();
-			if (result?.declaration?.type === 'EmptyStatement') {
-				return b.empty;
-			}
-			return result;
-		}
-
-		if (node.specifiers) {
-			const specifiers = node.specifiers.filter((/** @type {any} */ s) => s.exportKind !== 'type');
-			if (specifiers.length === 0) return b.empty;
-
-			return { ...node, specifiers };
-		}
-
-		return node;
-	},
-	ExportDefaultDeclaration(node) {
-		if (node.exportKind === 'type') return b.empty;
-		return node;
-	},
-	ExportAllDeclaration(node) {
-		if (node.exportKind === 'type') return b.empty;
-		return node;
-	},
-	PropertyDefinition(node, { next }) {
-		if (node.accessor) {
-			e.typescript_invalid_feature(
-				node,
-				'accessor fields (related TSC proposal is not stage 4 yet)'
-			);
-		}
-		return next();
-	},
-	TSAsExpression(node, context) {
-		return context.visit(node.expression);
-	},
-	TSSatisfiesExpression(node, context) {
-		return context.visit(node.expression);
-	},
-	TSNonNullExpression(node, context) {
-		return context.visit(node.expression);
-	},
-	TSInterfaceDeclaration() {
-		return b.empty;
-	},
-	TSTypeAliasDeclaration() {
-		return b.empty;
-	},
-	TSTypeAssertion(node, context) {
-		return context.visit(node.expression);
-	},
-	TSEnumDeclaration(node) {
-		e.typescript_invalid_feature(node, 'enums');
-	},
-	TSParameterProperty(node, context) {
-		if ((node.readonly || node.accessibility) && context.path.at(-2)?.kind === 'constructor') {
-			e.typescript_invalid_feature(node, 'accessibility modifiers on constructor parameters');
-		}
-		return context.visit(node.parameter);
-	},
-	TSInstantiationExpression(node, context) {
-		return context.visit(node.expression);
-	},
-	FunctionExpression: remove_this_param,
-	FunctionDeclaration: remove_this_param,
-	TSDeclareFunction() {
-		return b.empty;
-	},
-	ClassBody(node, context) {
-		const body = [];
-		for (const _child of node.body) {
-			const child = context.visit(_child);
-			if (child.type !== 'PropertyDefinition' || !child.declare) {
-				body.push(child);
-			}
-		}
-		return {
-			...node,
-			body
-		};
-	},
-	ClassDeclaration(node, context) {
-		if (node.declare) {
-			return b.empty;
-		}
-		delete node.abstract;
-		delete node.implements;
-		delete node.superTypeArguments;
-		delete node.superTypeParameters;
-		return context.next();
-	},
-	ClassExpression(node, context) {
-		delete node.implements;
-		delete node.superTypeArguments;
-		delete node.superTypeParameters;
-		return context.next();
-	},
-	MethodDefinition(node, context) {
-		if (node.abstract) {
-			return b.empty;
-		}
-		return context.next();
-	},
-	VariableDeclaration(node, context) {
-		if (node.declare) {
-			return b.empty;
-		}
-		return context.next();
-	},
-	TSModuleDeclaration(node, context) {
-		if (!node.body) return b.empty;
-
-		// namespaces can contain non-type nodes
-		const cleaned = /** @type {any[]} */ (node.body.body).map((entry) => context.visit(entry));
-		if (cleaned.some((entry) => entry !== b.empty)) {
-			e.typescript_invalid_feature(node, 'namespaces with non-type nodes');
-		}
-
-		return b.empty;
-	}
-};
-
-/**
- * @template T
- * @param {T} ast
- * @returns {T}
- */
-export function remove_typescript_nodes(ast) {
-	return walk(ast, null, visitors);
-}
diff --git a/packages/svelte/src/compiler/phases/1-parse/state/tag.js b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
index 60e8afa777..1c556b744d 100644
--- a/packages/svelte/src/compiler/phases/1-parse/state/tag.js
+++ b/packages/svelte/src/compiler/phases/1-parse/state/tag.js
@@ -417,8 +417,8 @@ function open(parser) {
 				e.expected_token(parser.template.length, ')');
 			}
 
-			const { params, end } = parse_params_at(parser, open);
-			parameters = params;
+			const { node, end } = parse_params_at(parser, open);
+			parameters = node;
 			parser.index = end;
 		}
 
diff --git a/packages/svelte/src/compiler/phases/2-analyze/index.js b/packages/svelte/src/compiler/phases/2-analyze/index.js
index 826d1d5415..9a79871992 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/index.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/index.js
@@ -260,7 +260,7 @@ export function analyze_module(source, options) {
 	const comments = [];
 
 	state.set_source(source);
-	const ast = parse(source, comments, false, false);
+	const ast = parse(source, comments, false);
 
 	const { scope, scopes, has_await } = create_scopes(ast, new ScopeRoot(), false, null);
 
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/PropertyDefinition.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/PropertyDefinition.js
index 99d05cb47c..d2f9395420 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/PropertyDefinition.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/PropertyDefinition.js
@@ -8,6 +8,10 @@ import { get_name } from '../../nodes.js';
  * @param {Context} context
  */
 export function PropertyDefinition(node, context) {
+	if (/** @type {any} */ (node).accessor) {
+		e.typescript_invalid_feature(node, 'accessor fields (related TSC proposal is not stage 4 yet)');
+	}
+
 	const name = get_name(node.key);
 	const field = name && context.state.state_fields.get(name);