From 7f60941367d07600051b540c02c0875911736dec Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <boopathi@users.noreply.github.com>
Date: Mon, 23 Jan 2017 17:36:00 +0100
Subject: [PATCH] Remove undef from seqExpr - (Fix #373) (#388)

---
 ...-plugin-transform-remove-undefined-test.js | 32 +++++++++++++++++++
 .../src/index.js                              | 18 +++++++++++
 2 files changed, 50 insertions(+)

diff --git a/packages/babel-plugin-transform-remove-undefined/__tests__/babel-plugin-transform-remove-undefined-test.js b/packages/babel-plugin-transform-remove-undefined/__tests__/babel-plugin-transform-remove-undefined-test.js
index 6320a17cb..b5bde00f1 100644
--- a/packages/babel-plugin-transform-remove-undefined/__tests__/babel-plugin-transform-remove-undefined-test.js
+++ b/packages/babel-plugin-transform-remove-undefined/__tests__/babel-plugin-transform-remove-undefined-test.js
@@ -171,4 +171,36 @@ describe("transform-remove-undefined-plugin", () => {
       }`);
     expect(transform(source)).toBe(source);
   });
+
+  it("should remove from sequence expressions", () => {
+    const source = unpad(`
+      a = b, void 0, b = c, d.e.f(), void 0, hello.world();
+    `);
+    const expected = unpad(`
+      a = b, b = c, d.e.f(), hello.world();
+    `);
+    expect(transform(source)).toBe(expected);
+  });
+
+  it("should NOT remove last undefined from sequence expressions", () => {
+    const source = unpad(`
+      if (foo.bar(), void 0) {
+        foo.baz();
+      }
+      function bar() {
+        return a.b(), void 0;
+      }
+    `);
+    expect(transform(source)).toBe(source);
+  });
+
+  it("should remove last undefined from sequence expressions if safe", () => {
+    const source = unpad(`
+      a = b, void 0, b = c, d.e.f(), void 0, hello.world(), void 0;
+    `);
+    const expected = unpad(`
+      a = b, b = c, d.e.f(), hello.world();
+    `);
+    expect(transform(source)).toBe(expected);
+  });
 });
diff --git a/packages/babel-plugin-transform-remove-undefined/src/index.js b/packages/babel-plugin-transform-remove-undefined/src/index.js
index 571f65303..e6eb1942f 100644
--- a/packages/babel-plugin-transform-remove-undefined/src/index.js
+++ b/packages/babel-plugin-transform-remove-undefined/src/index.js
@@ -80,6 +80,24 @@ module.exports = function() {
   return {
     name: "transform-remove-undefined",
     visitor: {
+      SequenceExpression(path) {
+        const expressions = path.get("expressions");
+
+        for (let i = 0; i < expressions.length; i++) {
+          const expr = expressions[i];
+          if (!isPureAndUndefined(expr)) continue;
+
+          // last value
+          if (i === expressions.length - 1) {
+            if (path.parentPath.isExpressionStatement()) {
+              expr.remove();
+            }
+          } else {
+            expr.remove();
+          }
+        }
+      },
+
       ReturnStatement(path) {
         if (path.node.argument !== null) {
           if (isPureAndUndefined(path.get("argument"))) {