Support IE in fallback JavaScript

Author: literalpie

Sources/swift-doc/Subcommands/Generate.swift

@@ -147,10 +147,15 @@ func fetchRemoteJS() throws -> Data {
   let jsURL = Bundle.module.url(forResource: "all", withExtension: "js")!
   return try Data(contentsOf: jsURL)
   #else
-  return Data("""
-  window.addEventListener("load", ()=>{
+  // When using Swift Package Manager versions that don't support bundled resources, just hide the theme select drop-down.
+  let fallbackJS = """
+  var hideThemeSelect = function() {
     document.querySelector(".theme-select-container").hidden = true;
-  })
-  """.utf8)
+  }
+  // hiding the element in `requestAnimationFrame` causes the function to be called after the element exists, 
+  // but fast enough that the element does not flash on the screen.
+  window.requestAnimationFrame(hideThemeSelect)
+  """
+  return Data(fallbackJS.utf8)
   #endif
 }