remove pre-existing sourcemap comments

src/Module.js

@@ -41,6 +41,13 @@ export default class Module {
 			filename: id
 		});
 
+		// remove existing sourceMappingURL comments
+		const pattern = /\/\/#\s+sourceMappingURL=.+\n?/g;
+		let match;
+		while ( match = pattern.exec( source ) ) {
+			this.magicString.remove( match.index, match.index + match[0].length );
+		}
+
 		this.suggestedNames = blank();
 		this.comments = [];
 

test/form/removes-existing-sourcemap-comments/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'removes existing sourcemap comments'
+};

test/form/removes-existing-sourcemap-comments/_expected/amd.js

@@ -0,0 +1,9 @@
+define(function () { 'use strict';
+
+	function foo () {
+		return 42;
+	}
+
+	console.log( foo() );
+
+});

test/form/removes-existing-sourcemap-comments/_expected/cjs.js

@@ -0,0 +1,7 @@
+'use strict';
+
+function foo () {
+	return 42;
+}
+
+console.log( foo() );

test/form/removes-existing-sourcemap-comments/_expected/es6.js

@@ -0,0 +1,5 @@
+function foo () {
+	return 42;
+}
+
+console.log( foo() );

test/form/removes-existing-sourcemap-comments/_expected/iife.js

@@ -0,0 +1,9 @@
+(function () { 'use strict';
+
+	function foo () {
+		return 42;
+	}
+
+	console.log( foo() );
+
+})();

test/form/removes-existing-sourcemap-comments/_expected/umd.js

@@ -0,0 +1,13 @@
+(function (global, factory) {
+	typeof exports === 'object' && typeof module !== 'undefined' ? factory() :
+	typeof define === 'function' && define.amd ? define(factory) :
+	factory();
+}(this, function () { 'use strict';
+
+	function foo () {
+		return 42;
+	}
+
+	console.log( foo() );
+
+}));