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

djpohly · web-flow · commit da31b0139c4e · 2022-08-09T12:38:57.000+08:00
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);")

Original file line number	Diff line number	Diff line change
`@@ -309,6 +309,11 @@ function _evaluate(path: NodePath, state: State): any {`
`309`	`309`	`if (!state.confident) return;`
`310`	`310`
`311`	`311`	`return left && right;`
	`312`	`+ case "??":`
	`313`	`+ state.confident = leftConfident && (left != null \|\| rightConfident);`
	`314`	`+ if (!state.confident) return;`
	`315`	`+`
	`316`	`+ return left ?? right;`
`312`	`317`	`}`
`313`	`318`	`}`
`314`	`319`