JavaScriptSG: fix broken generation of enum literals

Related to kaitai-io/kaitai_struct#1074

Until this commit, any generated JS test spec from a `.kst` file
containing an enum literal would have a syntax error because of lines
like `const ./Enum0 = require(...);`. It seems that this bug exists
since 66e75b3. In that commit, I tried
to fix the build error of KST translator due to the compiler API change
in kaitai-io/kaitai_struct_compiler@8007e0e#diff-6164bdf7b558cea6ff36b4a50508205a4569f8e98e398e77c4373679fceafffa.
In JavaScriptSG, I just passed the existing `importList` to
JavaScriptTranslator without thinking about the consequences (which were
exactly the illegal `const ./Enum0 = require(...);` lines). This should
now be fixed.

translator/src/main/scala/io/kaitai/struct/testtranslator/specgenerators/JavaScriptSG.scala

@@ -1,6 +1,6 @@
 package io.kaitai.struct.testtranslator.specgenerators
 
-import _root_.io.kaitai.struct.ClassTypeProvider
+import _root_.io.kaitai.struct.{ClassTypeProvider, ImportList}
 import _root_.io.kaitai.struct.datatype.{DataType, KSError}
 import _root_.io.kaitai.struct.datatype.DataType.BytesType
 import _root_.io.kaitai.struct.exprlang.Ast
@@ -10,7 +10,24 @@ import _root_.io.kaitai.struct.translators.JavaScriptTranslator
 
 class JavaScriptSG(spec: TestSpec, provider: ClassTypeProvider) extends BaseGenerator(spec) {
   val className = JavaScriptCompiler.type2class(spec.id)
-  val translator = new JavaScriptTranslator(provider, importList)
+  // JavaScriptTranslator accepts an ImportList so that if it translates an enum
+  // literal referencing an external enum (e.g. `external_spec::enum::label`),
+  // it can generate an import of the .ksy module in which the enum is defined.
+  // We don't pass our main `importList` and instead create a separate
+  // ImportList, because we don't want to output these imports at the top level.
+  // The reason is that they might refer to generated parsers that don't exist
+  // or contain syntax errors because of KSC bugs, and if a top-level
+  // `require()` fails, then the test spec "crashes" without the test framework
+  // having a clue what test it was).
+  //
+  // For now, we use `spec.extraImports` (i.e. the manually specified `imports`
+  // in the .kst spec) in runParse() instead, which we can output into the test
+  // body (which means that `require()` failures will be assigned correctly to
+  // the specific test). We cannot use `translatorImportList` there because it
+  // will still be empty at that point - some refactoring would be needed to use
+  // it instead of `spec.extraImports`.
+  val translatorImportList = new ImportList()
+  val translator = new JavaScriptTranslator(provider, translatorImportList)
 
   importList.add("assert")
 
@@ -21,11 +38,12 @@ class JavaScriptSG(spec: TestSpec, provider: ClassTypeProvider) extends BaseGene
   override def runParse(): Unit = {
     importList.add("testHelper")
 
-    out.puts(s"testHelper('$className', 'src/${spec.data}', function(r, $className) {")
+    out.puts(s"testHelper('$className', 'src/${spec.data}', function(r, ${className}_) {")
     out.inc
+    // TODO: replace `spec.extraImports` with `translatorImportList` (see comment above)
     spec.extraImports.foreach { (entry) =>
       val entryClass = JavaScriptCompiler.type2class(entry)
-      out.puts(s"var $entryClass = require('$entryClass').$entryClass;")
+      out.puts(s"var ${entryClass}_ = require('$entryClass');")
     }
   }