Add support for static evaluation of ?? operator (#14837)

babel · Aug 9, 2022 · da31b01 · da31b01
1 parent e2442e1
commit da31b01
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diff --git a/packages/babel-traverse/src/path/evaluation.ts b/packages/babel-traverse/src/path/evaluation.ts
@@ -309,6 +309,11 @@ function _evaluate(path: NodePath, state: State): any {
         if (!state.confident) return;
 
         return left && right;
+      case "??":
+        state.confident = leftConfident && (left != null || rightConfident);
+        if (!state.confident) return;
+
+        return left ?? right;
     }
   }
 

diff --git a/packages/babel-traverse/test/evaluation.js b/packages/babel-traverse/test/evaluation.js
@@ -68,6 +68,14 @@ describe("evaluation", function () {
     expect(getPath("0 && x === 'y'").get("body")[0].evaluate().value).toBe(0);
   });
 
+  it("should handle ??", function () {
+    expect(getPath("null ?? 42").get("body")[0].evaluate().value).toBe(42);
+    expect(getPath("void 0 ?? 42").get("body")[0].evaluate().value).toBe(42);
+    expect(getPath("0 ?? 42").get("body")[0].evaluate().value).toBe(0);
+    expect(getPath("x ?? 42").get("body")[0].evaluate().confident).toBe(false);
+    expect(getPath("42 ?? x === 'y'").get("body")[0].evaluate().value).toBe(42);
+  });
+
   it("should work with repeated, indeterminate identifiers", function () {
     expect(
       getPath("var num = foo(); (num > 0 && num < 100);")