Replace typeof before DCE

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

@@ -693,31 +693,6 @@ impl<'a> Fold for Hoist<'a> {
           }
         }
       }
-      Expr::Unary(ref unary) => {
-        // typeof require -> "function"
-        // typeof module -> "object"
-        if unary.op == UnaryOp::TypeOf {
-          if let Expr::Ident(ident) = &*unary.arg {
-            if ident.sym == js_word!("require") && !self.collect.decls.contains(&id!(ident)) {
-              return Expr::Lit(Lit::Str(Str {
-                kind: StrKind::Synthesized,
-                has_escape: false,
-                span: unary.span,
-                value: js_word!("function"),
-              }));
-            }
-
-            if ident.sym == js_word!("module") && !self.collect.decls.contains(&id!(ident)) {
-              return Expr::Lit(Lit::Str(Str {
-                kind: StrKind::Synthesized,
-                has_escape: false,
-                span: unary.span,
-                value: js_word!("object"),
-              }));
-            }
-          }
-        }
-      }
       _ => {}
     }
 

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

@@ -18,6 +18,7 @@ mod fs;
 mod global_replacer;
 mod hoist;
 mod modules;
+mod typeof_replacer;
 mod utils;
 
 use std::collections::{HashMap, HashSet};
@@ -49,6 +50,7 @@ use fs::inline_fs;
 use global_replacer::GlobalReplacer;
 use hoist::{hoist, CollectResult, HoistResult};
 use modules::esm2cjs;
+use typeof_replacer::*;
 use utils::{CodeHighlight, Diagnostic, DiagnosticSeverity, SourceLocation, SourceType};
 
 use crate::hoist::Collect;
@@ -321,6 +323,10 @@ pub fn transform(config: Config) -> Result<TransformResult, std::io::Error> {
             let mut diagnostics = vec![];
             let module = {
               let mut passes = chain!(
+                Optional::new(
+                  TypeofReplacer { decls: &decls },
+                  config.source_type != SourceType::Script
+                ),
                 // Inline process.env and process.browser
                 Optional::new(
                   EnvReplacer {

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

@@ -0,0 +1,52 @@
+use std::collections::HashSet;
+
+use swc_atoms::JsWord;
+use swc_ecmascript::ast::{Expr, Lit, Str, StrKind, UnaryOp};
+use swc_ecmascript::visit::{Fold, FoldWith};
+
+use crate::id;
+use crate::utils::IdentId;
+
+pub struct TypeofReplacer<'a> {
+  pub decls: &'a HashSet<IdentId>,
+}
+
+impl<'a> Fold for TypeofReplacer<'a> {
+  fn fold_expr(&mut self, node: Expr) -> Expr {
+    if let Expr::Unary(ref unary) = node {
+      // typeof require -> "function"
+      // typeof module -> "object"
+      if unary.op == UnaryOp::TypeOf {
+        if let Expr::Ident(ident) = &*unary.arg {
+          if ident.sym == js_word!("require") && !self.decls.contains(&id!(ident)) {
+            return Expr::Lit(Lit::Str(Str {
+              kind: StrKind::Synthesized,
+              has_escape: false,
+              span: unary.span,
+              value: js_word!("function"),
+            }));
+          }
+          let exports: JsWord = "exports".into();
+          if ident.sym == exports && !self.decls.contains(&id!(ident)) {
+            return Expr::Lit(Lit::Str(Str {
+              kind: StrKind::Synthesized,
+              has_escape: false,
+              span: unary.span,
+              value: js_word!("object"),
+            }));
+          }
+
+          if ident.sym == js_word!("module") && !self.decls.contains(&id!(ident)) {
+            return Expr::Lit(Lit::Str(Str {
+              kind: StrKind::Synthesized,
+              has_escape: false,
+              span: unary.span,
+              value: js_word!("object"),
+            }));
+          }
+        }
+      }
+    }
+    node.fold_children_with(self)
+  }
+}