JsModule {
    bom_token: missing (optional),
    interpreter_token: missing (optional),
    directives: JsDirectiveList [],
    items: JsModuleItemList [
        JsClassDeclaration {
            decorators: JsDecoratorList [],
            abstract_token: missing (optional),
            class_token: CLASS_KW@0..6 "class" [] [Whitespace(" ")],
            id: JsIdentifierBinding {
                name_token: IDENT@6..8 "A" [] [Whitespace(" ")],
            },
            type_parameters: missing (optional),
            extends_clause: missing (optional),
            implements_clause: missing (optional),
            l_curly_token: L_CURLY@8..9 "{" [] [],
            members: JsClassMemberList [
                JsBogusMember {
                    items: [
                        L_BRACK@9..15 "[" [Newline("\n"), Whitespace("    ")] [],
                        TsIndexSignatureParameter {
                            binding: JsIdentifierBinding {
                                name_token: IDENT@15..16 "a" [] [],
                            },
                            type_annotation: TsTypeAnnotation {
                                colon_token: COLON@16..18 ":" [] [Whitespace(" ")],
                                ty: TsNumberType {
                                    number_token: NUMBER_KW@18..24 "number" [] [],
                                },
                            },
                        },
                        R_BRACK@24..25 "]" [] [],
                        TsTypeAnnotation {
                            colon_token: COLON@25..27 ":" [] [Whitespace(" ")],
                            ty: TsStringType {
                                string_token: STRING_KW@27..33 "string" [] [],
                            },
                        },
                        SEMICOLON@33..34 ";" [] [],
                    ],
                },
            ],
            r_curly_token: R_CURLY@34..36 "}" [Newline("\n")] [],
        },
    ],
    eof_token: EOF@36..37 "" [Newline("\n")] [],
}

0: JS_MODULE@0..37
  0: (empty)
  1: (empty)
  2: JS_DIRECTIVE_LIST@0..0
  3: JS_MODULE_ITEM_LIST@0..36
    0: JS_CLASS_DECLARATION@0..36
      0: JS_DECORATOR_LIST@0..0
      1: (empty)
      2: CLASS_KW@0..6 "class" [] [Whitespace(" ")]
      3: JS_IDENTIFIER_BINDING@6..8
        0: IDENT@6..8 "A" [] [Whitespace(" ")]
      4: (empty)
      5: (empty)
      6: (empty)
      7: L_CURLY@8..9 "{" [] []
      8: JS_CLASS_MEMBER_LIST@9..34
        0: JS_BOGUS_MEMBER@9..34
          0: L_BRACK@9..15 "[" [Newline("\n"), Whitespace("    ")] []
          1: TS_INDEX_SIGNATURE_PARAMETER@15..24
            0: JS_IDENTIFIER_BINDING@15..16
              0: IDENT@15..16 "a" [] []
            1: TS_TYPE_ANNOTATION@16..24
              0: COLON@16..18 ":" [] [Whitespace(" ")]
              1: TS_NUMBER_TYPE@18..24
                0: NUMBER_KW@18..24 "number" [] []
          2: R_BRACK@24..25 "]" [] []
          3: TS_TYPE_ANNOTATION@25..33
            0: COLON@25..27 ":" [] [Whitespace(" ")]
            1: TS_STRING_TYPE@27..33
              0: STRING_KW@27..33 "string" [] []
          4: SEMICOLON@33..34 ";" [] []
      9: R_CURLY@34..36 "}" [Newline("\n")] []
  4: EOF@36..37 "" [Newline("\n")] []
--
index_signature_class_member_in_js.js:2:5 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  × Index signatures are a TypeScript only feature. Convert your file to a TypeScript file or remove the syntax.
  
    1 │ class A {
  > 2 │     [a: number]: string;
      │     ^^^^^^^^^^^^^^^^^^^^
    3 │ }
    4 │ 
  
  i TypeScript only syntax
  
--
class A {
    [a: number]: string;
}