EmitHost is a just a simplified (as in narrowed down) version of CompilerHost (and is at runtime actually a CompilerHost for many use cases).

  1. emitFiles ->
  2.     emitFile(jsFilePath, targetSourceFile) ->
  3.         emitJavaScript(jsFilePath, targetSourceFile);

There is a lot of good comments in this function so we present it below :

  1. function emitSourceFile(sourceFile: SourceFile): void {
  2.     currentSourceFile = sourceFile;
  3.     exportFunctionForFile = undefined;
  4.     emit(sourceFile);

The emit function handles comment emit + actual JavaScript emit. The actual JavaScript emit is the job of emitJavaScriptWorker function.

Recursion is done by simply calling other emitFoo function from these functions as needed e.g. from emitFunctionDeclaration :

  1. function emitFunctionDeclaration(node: FunctionLikeDeclaration) {
  2.     if (nodeIsMissing(node.body)) {
  3.         return emitOnlyPinnedOrTripleSlashComments(node);
  4.     }
  6.         // Methods will emit the comments as part of emitting method declaration
  7.         emitLeadingComments(node);
  8.     }
  10.     // For targeting below es6, emit functions-like declaration including arrow function using function keyword.
  11.     // When targeting ES6, emit arrow function natively in ES6 by omitting function keyword and using fat arrow instead
  12.     if (!shouldEmitAsArrowFunction(node)) {
  13.         if (isES6ExportedDeclaration(node)) {
  14.             write("export ");
  15.             if (node.flags & NodeFlags.Default) {
  17.             }
  18.         }
  20.         write("function");
  21.             write("*");
  22.         }
  23.         write(" ");
  24.     }
  26.     if (shouldEmitFunctionName(node)) {
  27.         emitDeclarationName(node);
  28.     }
  30.     emitSignatureAndBody(node);
  31.     if (languageVersion < ScriptTarget.ES6 && node.kind === SyntaxKind.FunctionDeclaration && node.parent === currentSourceFile && node.name) {
  32.         emitExportMemberAssignments((<FunctionDeclaration>node).name);
  33.     }
  34.     if (node.kind !== SyntaxKind.MethodDeclaration && node.kind !== SyntaxKind.MethodSignature) {
  35.         emitTrailingComments(node);