rollup · Rich-Harris · Aug 17, 2016 · Aug 16, 2016
diff --git a/src/Bundle.js b/src/Bundle.js
@@ -65,6 +65,7 @@ export default class Bundle {
 		this.externalModules = [];
 		this.internalNamespaces = [];
 
+		this.context = String( options.context );
 		this.assumedGlobals = blank();
 
 		if ( typeof options.external === 'function' ) {

diff --git a/src/Statement.js b/src/Statement.js
@@ -60,8 +60,8 @@ export default class Statement {
 				}
 
 				if ( node.type === 'ThisExpression' && contextDepth === 0 ) {
-					module.magicString.overwrite( node.start, node.end, 'undefined' );
-					module.bundle.onwarn( 'The `this` keyword is equivalent to `undefined` at the top level of an ES module, and has been rewritten' );
+					module.magicString.overwrite( node.start, node.end, module.bundle.context );
+					if ( module.bundle.context === 'undefined' ) module.bundle.onwarn( 'The `this` keyword is equivalent to `undefined` at the top level of an ES module, and has been rewritten' );
 				}
 
 				if ( node._scope ) scope = node._scope;

diff --git a/src/rollup.js b/src/rollup.js
@@ -12,6 +12,7 @@ const ALLOWED_KEYS = [
 	'acorn',
 	'banner',
 	'cache',
+	'context',
 	'dest',
 	'entry',
 	'exports',

diff --git a/test/form/custom-context/_config.js b/test/form/custom-context/_config.js
@@ -0,0 +1,6 @@
+module.exports = {
+	description: 'allows custom context',
+	options: {
+		context: `lolwut`
+	}
+};
diff --git a/test/form/custom-context/_expected/amd.js b/test/form/custom-context/_expected/amd.js
@@ -0,0 +1,5 @@
+define(function () { 'use strict';
+
+	lolwut.prop = '???';
+
+});
diff --git a/test/form/custom-context/_expected/cjs.js b/test/form/custom-context/_expected/cjs.js
@@ -0,0 +1,3 @@
+'use strict';
+
+lolwut.prop = '???';
diff --git a/test/form/custom-context/_expected/es.js b/test/form/custom-context/_expected/es.js
@@ -0,0 +1 @@
+lolwut.prop = '???';
diff --git a/test/form/custom-context/_expected/iife.js b/test/form/custom-context/_expected/iife.js
@@ -0,0 +1,6 @@
+(function () {
+	'use strict';
+
+	lolwut.prop = '???';
+
+}());
diff --git a/test/form/custom-context/_expected/umd.js b/test/form/custom-context/_expected/umd.js
@@ -0,0 +1,9 @@
+(function (global, factory) {
+	typeof exports === 'object' && typeof module !== 'undefined' ? factory() :
+	typeof define === 'function' && define.amd ? define(factory) :
+	(factory());
+}(this, (function () { 'use strict';
+
+	lolwut.prop = '???';
+
+})));
diff --git a/test/form/custom-context/main.js b/test/form/custom-context/main.js
@@ -0,0 +1 @@
+this.prop = '???';
diff --git a/test/test.js b/test/test.js
@@ -89,7 +89,7 @@ describe( 'rollup', function () {
 			return rollup.rollup({ entry: 'x', plUgins: [] }).then( () => {
 				throw new Error( 'Missing expected error' );
 			}, err => {
-				assert.equal( err.message, 'Unexpected key \'plUgins\' found, expected one of: acorn, banner, cache, dest, entry, exports, external, footer, format, globals, indent, intro, moduleId, moduleName, noConflict, onwarn, outro, paths, plugins, preferConst, sourceMap, sourceMapFile, targets, treeshake, useStrict' );
+				assert.equal( err.message, 'Unexpected key \'plUgins\' found, expected one of: acorn, banner, cache, context, dest, entry, exports, external, footer, format, globals, indent, intro, moduleId, moduleName, noConflict, onwarn, outro, paths, plugins, preferConst, sourceMap, sourceMapFile, targets, treeshake, useStrict' );
 			});
 		});
 	});