Use the '__assign' helper in transforms.

src/compiler/factory.ts

@@ -822,16 +822,6 @@ namespace ts {
         return react;
     }
 
-    export function createReactSpread(reactNamespace: string, segments: Expression[], parentElement: JsxOpeningLikeElement) {
-        return createCall(
-            createPropertyAccess(
-                createReactNamespace(reactNamespace, parentElement),
-                "__spread"
-            ),
-            segments
-        );
-    }
-
     export function createReactCreateElement(reactNamespace: string, tagName: Expression, props: Expression, children: Expression[], parentElement: JsxOpeningLikeElement, location: TextRange): LeftHandSideExpression {
         const argumentsList = [tagName];
         if (props) {
@@ -868,6 +858,13 @@ namespace ts {
         );
     }
 
+    export function createAssignHelper(attributesSegments: Expression[]) {
+        return createCall(
+            createIdentifier("__assign"),
+            attributesSegments
+        );
+    }
+
     export function createParamHelper(expression: Expression, parameterOffset: number) {
         return createCall(
             createIdentifier("__param"),

src/compiler/printer.ts

@@ -26,6 +26,19 @@ var __extends = (this && this.__extends) || function (d, b) {
     d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
 };`;
 
+        // Emit output for the __assign helper function.
+        // This is typically used for JSX spread attributes,
+        // and can be used for object literal spread properties.
+        const assignHelper = `
+var __assign = (this && this.__assign) || Object.assign || function(t) {
+    for (var s, i = 1, n = arguments.length; i < n; i++) {
+        s = arguments[i];
+        for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p))
+            t[p] = s[p];
+    }
+    return t;
+};`;
+
         // emit output for the __decorate helper function
         const decorateHelper = `
 var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
@@ -173,6 +186,7 @@ const _super = (function (geti, seti) {
             let currentText: string;
             let currentFileIdentifiers: Map<string>;
             let extendsEmitted: boolean;
+            let assignEmitted: boolean;
             let decorateEmitted: boolean;
             let paramEmitted: boolean;
             let awaiterEmitted: boolean;
@@ -232,6 +246,7 @@ const _super = (function (geti, seti) {
                 currentSourceFile = undefined;
                 currentText = undefined;
                 extendsEmitted = false;
+                assignEmitted = false;
                 decorateEmitted = false;
                 paramEmitted = false;
                 awaiterEmitted = false;
@@ -2023,6 +2038,11 @@ const _super = (function (geti, seti) {
                         helpersEmitted = true;
                     }
 
+                    if (compilerOptions.jsx !== JsxEmit.Preserve && !assignEmitted && (node.flags & NodeFlags.HasJsxSpreadAttribute)) {
+                        writeLines(assignHelper);
+                        assignEmitted = true;
+                    }
+
                     if (!decorateEmitted && node.flags & NodeFlags.HasDecorators) {
                         writeLines(decorateHelper);
                         if (compilerOptions.emitDecoratorMetadata) {

src/compiler/transformers/jsx.ts

@@ -100,9 +100,9 @@ namespace ts {
                 }
 
                 // Either emit one big object literal (no spread attribs), or
-                // a call to React.__spread
+                // a call to the __assign helper.
                 objectProperties = singleOrUndefined(segments)
-                    || createReactSpread(compilerOptions.reactNamespace, segments, node);
+                    || createAssignHelper(segments);
             }
 
             const element = createReactCreateElement(