babel/babel · error · Error

Decorating two elements with the same name (${desc[key].name

Error message

Decorating two elements with the same name (${desc[key].name}) is not supported yet

What it means

Thrown inside applyDecs2311 when two non-field, non-private class elements sharing the same name are both decorated, and they are not a complementary getter/setter pair (the flag^kind check `!== 7` distinguishes a get+set pair from a duplicate). The current decorator runtime does not support decorating two distinct elements with the same name beyond an accessor get/set duo, so it aborts rather than silently dropping a decorator.

Source

Thrown at packages/babel-helpers/src/helpers/applyDecs2311.ts:344

            },
          };
        } else {
          desc[key] = decVal;
        }

        if (!isField) {
          setFunctionName(desc[key], name, isMethod ? "" : key);
        }
      } else if (!isField) {
        desc = Object.getOwnPropertyDescriptor(Class, name)!;
      }

      if (!isField && !isPrivate) {
        _ = existingNonFields[+isStatic!][name];
        // flag is 1, 3, or 4; kind is 0, 1, 2, 3, or 4
        // flag ^ kind is 7 if and only if one of them is 3 and the other one is 4.
        if (_ && (_ ^ kind) !== 7) {
          throw new Error(
            "Decorating two elements with the same name (" +
              desc[key].name +
              ") is not supported yet",
          );
        }
        // We use PROP_KIND.ACCESSOR to mark a name as "fully used":
        // either a get/set pair, or a non-getter/setter.
        existingNonFields[+isStatic!][name] =
          kind < PROP_KIND.GETTER
            ? PROP_KIND.ACCESSOR
            : (kind as PROP_KIND.GETTER | PROP_KIND.SETTER);
      }
    }

    var newValue = Class;

    for (var i = decs.length - 1; i >= 0; i -= decoratorsHaveThis ? 2 : 1) {
      var dec = assertCallable(decs[i], "A decorator", "be", true) as Function,

View on GitHub (pinned to 1eac448147)

Solutions

Rename one of the colliding decorated elements so names are unique.
Remove the decorator from the shadowed element if only one should take effect.
If you intended a getter/setter pair, ensure they are decorated as `accessor`/get+set, not two methods.
Audit the class for accidental duplicate method declarations introduced during a merge.

Example fix

// before
class C {
  @dec handle() {}
  @dec handle() {} // duplicate name
}
// after
class C {
  @dec handleClick() {}
  @dec handleTouch() {}
}

Defensive patterns

Strategy: validation

Validate before calling

// Detect duplicate decorated element names at author time
function findDuplicateDecoratedNames(classBody) {
  const seen = new Map();
  const dups = [];
  for (const el of classBody) {
    if (el.decorators?.length && el.key) {
      if (seen.has(el.key)) dups.push(el.key);
      seen.set(el.key, el.kind);
    }
  }
  return dups;
}

Prevention

Use unique names for decorated class elements.
Run a lint pass that flags duplicate method names within a class body.
Review merge commits for accidental duplicate method declarations.

When it happens

Trigger: A class declares two methods with the same name (one shadowing the other) and both carry decorators, or a method and a getter with the same name both decorated. The check at line 343 (_ && (_ ^ kind) !== 7) fires for the second decorated element after existingNonFields already recorded the first.

Common situations: Refactoring that accidentally creates duplicate method names while decorators are attached, or merging mixin definitions that collide on a name. Also when a developer expects the second definition to win but both are decorated.

Related errors

AI-assisted analysis of babel/babel@1eac448147 (2026-08-08). Data as JSON: /api/errors/c09790f170ad9688. Report an issue: GitHub.