From 02b653c06116ca1ddcfefc1d713711868299c70f Mon Sep 17 00:00:00 2001
From: overlookmotel <557937+overlookmotel@users.noreply.github.com>
Date: Sun, 15 Dec 2024 16:55:00 +0000
Subject: [PATCH] feat(transformer/class-properties): do not create temp var
 for template literal computed key (#7919)

Do not create temp var for computed key which is `TemplateLiteral` with no expressions. Evaluating such a template literal cannot have side effects.

```js
class C {
  [`foo`] = 1;
}
```

But this *can* have side effects:

```js
class C {
  [`foo${bar}`] = 1;
}
```
---
 .../src/es2022/class_properties/computed_key.rs             | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/crates/oxc_transformer/src/es2022/class_properties/computed_key.rs b/crates/oxc_transformer/src/es2022/class_properties/computed_key.rs
index 3a088e7e9151c..3a4e7560d2a4e 100644
--- a/crates/oxc_transformer/src/es2022/class_properties/computed_key.rs
+++ b/crates/oxc_transformer/src/es2022/class_properties/computed_key.rs
@@ -112,6 +112,12 @@ fn key_needs_temp_var(key: &Expression, ctx: &TraverseCtx) -> bool {
         | Expression::BigIntLiteral(_)
         | Expression::RegExpLiteral(_)
         | Expression::StringLiteral(_) => false,
+        // Template literal cannot have side effects if it has no expressions.
+        // If it *does* have expressions, but they're all literals, then also cannot have side effects,
+        // but don't bother checking for that as it shouldn't occur in real world code.
+        // Why would you write "`x${9}z`" when you can just write "`x9z`"?
+        // Note: "`x${foo}`" *can* have side effects if `foo` is an object with a `valueOf` method.
+        Expression::TemplateLiteral(lit) => !lit.expressions.is_empty(),
         // `IdentifierReference`s can have side effects if is unbound.
         //
         // If var is mutated, it also needs a temp var, because of cases like