Feature: replace environmental variable with in binary expression

packages/core/integration-tests/test/integration/env-binary-in-expression/index.js

@@ -0,0 +1,7 @@
+const existVar = 'ABC' in process.env ? 'correct' : 'incorrect';
+const notExistVar = 'DEF' in process.env ? 'incorrect' : 'correct';
+
+module.exports = {
+  existVar,
+  notExistVar,
+};

packages/core/integration-tests/test/javascript.js

@@ -3081,6 +3081,29 @@ describe('javascript', function () {
     });
   });
 
+  it('should inline environment variables with in binary expression whose right branch is process.env and left branch is string literal', async function () {
+    let b = await bundle(
+      path.join(__dirname, '/integration/env-binary-in-expression/index.js'),
+      {
+        env: {ABC: 'any'},
+        defaultTargetOptions: {
+          engines: {
+            browsers: '>= 0.25%',
+          },
+        },
+      },
+    );
+
+    let contents = await outputFS.readFile(b.getBundles()[0].filePath, 'utf8');
+    assert(!contents.includes('process.env'));
+
+    let output = await run(b);
+    assert.deepEqual(output, {
+      existVar: 'correct',
+      notExistVar: 'correct',
+    });
+  });
+
   it('should insert environment variables from a file', async function () {
     let b = await bundle(
       path.join(__dirname, '/integration/env-file/index.js'),

packages/transformers/js/core/src/env_replacer.rs

@@ -41,6 +41,21 @@ impl<'a> Fold for EnvReplacer<'a> {
       }
     }
 
+    // Replace `'foo' in process.env` with a boolean.
+    match &node {
+      Expr::Bin(binary) if binary.op == BinaryOp::In => {
+        if let (Expr::Lit(Lit::Str(left)), Expr::Member(member)) = (&*binary.left, &*binary.right) {
+          if match_member_expr(member, vec!["process", "env"], self.decls) {
+            return Expr::Lit(Lit::Bool(Bool {
+              value: self.env.contains_key(&left.value),
+              span: DUMMY_SP,
+            }));
+          }
+        }
+      }
+      _ => {}
+    }
+
     if let Expr::Member(ref member) = node {
       if self.is_browser && match_member_expr(member, vec!["process", "browser"], self.decls) {
         return Expr::Lit(Lit::Bool(Bool {