From 6a00cbe0ab59924b51f07e9a5d2f37dae15746ea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hu=C3=A1ng=20J=C3=B9nli=C3=A0ng?= <jlhwung@gmail.com>
Date: Thu, 26 Mar 2020 16:54:50 -0400
Subject: [PATCH] fix: isIdentifierName should reject empty string (#11339)

---
 .../src/identifier.js                         |  2 +-
 .../test/identifier.spec.js                   | 22 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-helper-validator-identifier/test/identifier.spec.js

diff --git a/packages/babel-helper-validator-identifier/src/identifier.js b/packages/babel-helper-validator-identifier/src/identifier.js
index db0f0abb7d73..5088281bbf8e 100644
--- a/packages/babel-helper-validator-identifier/src/identifier.js
+++ b/packages/babel-helper-validator-identifier/src/identifier.js
@@ -98,5 +98,5 @@ export function isIdentifierName(name: string): boolean {
       return false;
     }
   }
-  return true;
+  return !isFirst;
 }
diff --git a/packages/babel-helper-validator-identifier/test/identifier.spec.js b/packages/babel-helper-validator-identifier/test/identifier.spec.js
new file mode 100644
index 000000000000..60a25cb57851
--- /dev/null
+++ b/packages/babel-helper-validator-identifier/test/identifier.spec.js
@@ -0,0 +1,22 @@
+import { isIdentifierName } from "..";
+
+describe("isIdentifierName", function() {
+  it("returns false if provided string is empty", function() {
+    expect(isIdentifierName("")).toBe(false);
+  });
+  it.each(["hello", "$", "ゆゆ式", "$20", "hello20", "_", "if"])(
+    "returns true if provided string %p is an IdentifierName",
+    function(word) {
+      expect(isIdentifierName(word)).toBe(true);
+    },
+  );
+  it.each(["+hello", "0$", "-ゆゆ式", "#_", "_#"])(
+    "returns false if provided string %p is not an IdentifierName",
+    function(word) {
+      expect(isIdentifierName(word)).toBe(false);
+    },
+  );
+  it("supports astral symbols", function() {
+    expect(isIdentifierName("x\uDB40\uDDD5")).toBe(true);
+  });
+});