Emitter Functions

emitFiles

Defined in emitter.ts here is the function signature:

// targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile?: SourceFile): EmitResult {

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

The most interesting call stack from emitFiles is the following:

emitFiles ->
emitFile(jsFilePath, targetSourceFile) ->
emitJavaScript(jsFilePath, targetSourceFile);

emitJavaScript

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

function emitJavaScript(jsFilePath: string, root?: SourceFile) {
let writer = createTextWriter(newLine);
let write = writer.write;
let writeTextOfNode = writer.writeTextOfNode;
let writeLine = writer.writeLine;
let increaseIndent = writer.increaseIndent;
let decreaseIndent = writer.decreaseIndent;
let currentSourceFile: SourceFile;
// name of an exporter function if file is a System external module
// System.register([...], function (<exporter>) {...})
// exporting in System modules looks like:
// export var x; ... x = 1
// =>
// var x;... exporter("x", x = 1)
let exportFunctionForFile: string;
let generatedNameSet: Map<string> = {};
let nodeToGeneratedName: string[] = [];
let computedPropertyNamesToGeneratedNames: string[];
let extendsEmitted = false;
let decorateEmitted = false;
let paramEmitted = false;
let awaiterEmitted = false;
let tempFlags = 0;
let tempVariables: Identifier[];
let tempParameters: Identifier[];
let externalImports: (ImportDeclaration | ImportEqualsDeclaration | ExportDeclaration)[];
let exportSpecifiers: Map<ExportSpecifier[]>;
let exportEquals: ExportAssignment;
let hasExportStars: boolean;
/** Write emitted output to disk */
let writeEmittedFiles = writeJavaScriptFile;
let detachedCommentsInfo: { nodePos: number; detachedCommentEndPos: number }[];
let writeComment = writeCommentRange;
/** Emit a node */
let emit = emitNodeWithoutSourceMap;
/** Called just before starting emit of a node */
let emitStart = function (node: Node) { };
/** Called once the emit of the node is done */
let emitEnd = function (node: Node) { };
/** Emit the text for the given token that comes after startPos
* This by default writes the text provided with the given tokenKind
* but if optional emitFn callback is provided the text is emitted using the callback instead of default text
* @param tokenKind the kind of the token to search and emit
* @param startPos the position in the source to start searching for the token
* @param emitFn if given will be invoked to emit the text instead of actual token emit */
let emitToken = emitTokenText;
/** Called to before starting the lexical scopes as in function/class in the emitted code because of node
* @param scopeDeclaration node that starts the lexical scope
* @param scopeName Optional name of this scope instead of deducing one from the declaration node */
let scopeEmitStart = function(scopeDeclaration: Node, scopeName?: string) { };
/** Called after coming out of the scope */
let scopeEmitEnd = function() { };
/** Sourcemap data that will get encoded */
let sourceMapData: SourceMapData;
if (compilerOptions.sourceMap || compilerOptions.inlineSourceMap) {
initializeEmitterWithSourceMaps();
}
if (root) {
// Do not call emit directly. It does not set the currentSourceFile.
emitSourceFile(root);
}
else {
forEach(host.getSourceFiles(), sourceFile => {
if (!isExternalModuleOrDeclarationFile(sourceFile)) {
emitSourceFile(sourceFile);
}
});
}
writeLine();
writeEmittedFiles(writer.getText(), /*writeByteOrderMark*/ compilerOptions.emitBOM);
return;
/// BUNCH OF LOCAL FUNCTIONS
}

Basically it sets up a bunch of locals (these functions form the bulk of emitter.ts) and then hands off to a local function emitSourceFile which kicks off the emit. The emitSourceFile function just sets up the currentSourceFile and in turn hands off to a local emit function.

function emitSourceFile(sourceFile: SourceFile): void {
currentSourceFile = sourceFile;
exportFunctionForFile = undefined;
emit(sourceFile);
}

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

emitJavaScriptWorker

The complete function:

function emitJavaScriptWorker(node: Node) {
// Check if the node can be emitted regardless of the ScriptTarget
switch (node.kind) {
case SyntaxKind.Identifier:
return emitIdentifier(<Identifier>node);
case SyntaxKind.Parameter:
return emitParameter(<ParameterDeclaration>node);
case SyntaxKind.MethodDeclaration:
case SyntaxKind.MethodSignature:
return emitMethod(<MethodDeclaration>node);
case SyntaxKind.GetAccessor:
case SyntaxKind.SetAccessor:
return emitAccessor(<AccessorDeclaration>node);
case SyntaxKind.ThisKeyword:
return emitThis(node);
case SyntaxKind.SuperKeyword:
return emitSuper(node);
case SyntaxKind.NullKeyword:
return write("null");
case SyntaxKind.TrueKeyword:
return write("true");
case SyntaxKind.FalseKeyword:
return write("false");
case SyntaxKind.NumericLiteral:
case SyntaxKind.StringLiteral:
case SyntaxKind.RegularExpressionLiteral:
case SyntaxKind.NoSubstitutionTemplateLiteral:
case SyntaxKind.TemplateHead:
case SyntaxKind.TemplateMiddle:
case SyntaxKind.TemplateTail:
return emitLiteral(<LiteralExpression>node);
case SyntaxKind.TemplateExpression:
return emitTemplateExpression(<TemplateExpression>node);
case SyntaxKind.TemplateSpan:
return emitTemplateSpan(<TemplateSpan>node);
case SyntaxKind.JsxElement:
case SyntaxKind.JsxSelfClosingElement:
return emitJsxElement(<JsxElement|JsxSelfClosingElement>node);
case SyntaxKind.JsxText:
return emitJsxText(<JsxText>node);
case SyntaxKind.JsxExpression:
return emitJsxExpression(<JsxExpression>node);
case SyntaxKind.QualifiedName:
return emitQualifiedName(<QualifiedName>node);
case SyntaxKind.ObjectBindingPattern:
return emitObjectBindingPattern(<BindingPattern>node);
case SyntaxKind.ArrayBindingPattern:
return emitArrayBindingPattern(<BindingPattern>node);
case SyntaxKind.BindingElement:
return emitBindingElement(<BindingElement>node);
case SyntaxKind.ArrayLiteralExpression:
return emitArrayLiteral(<ArrayLiteralExpression>node);
case SyntaxKind.ObjectLiteralExpression:
return emitObjectLiteral(<ObjectLiteralExpression>node);
case SyntaxKind.PropertyAssignment:
return emitPropertyAssignment(<PropertyDeclaration>node);
case SyntaxKind.ShorthandPropertyAssignment:
return emitShorthandPropertyAssignment(<ShorthandPropertyAssignment>node);
case SyntaxKind.ComputedPropertyName:
return emitComputedPropertyName(<ComputedPropertyName>node);
case SyntaxKind.PropertyAccessExpression:
return emitPropertyAccess(<PropertyAccessExpression>node);
case SyntaxKind.ElementAccessExpression:
return emitIndexedAccess(<ElementAccessExpression>node);
case SyntaxKind.CallExpression:
return emitCallExpression(<CallExpression>node);
case SyntaxKind.NewExpression:
return emitNewExpression(<NewExpression>node);
case SyntaxKind.TaggedTemplateExpression:
return emitTaggedTemplateExpression(<TaggedTemplateExpression>node);
case SyntaxKind.TypeAssertionExpression:
return emit((<TypeAssertion>node).expression);
case SyntaxKind.AsExpression:
return emit((<AsExpression>node).expression);
case SyntaxKind.ParenthesizedExpression:
return emitParenExpression(<ParenthesizedExpression>node);
case SyntaxKind.FunctionDeclaration:
case SyntaxKind.FunctionExpression:
case SyntaxKind.ArrowFunction:
return emitFunctionDeclaration(<FunctionLikeDeclaration>node);
case SyntaxKind.DeleteExpression:
return emitDeleteExpression(<DeleteExpression>node);
case SyntaxKind.TypeOfExpression:
return emitTypeOfExpression(<TypeOfExpression>node);
case SyntaxKind.VoidExpression:
return emitVoidExpression(<VoidExpression>node);
case SyntaxKind.AwaitExpression:
return emitAwaitExpression(<AwaitExpression>node);
case SyntaxKind.PrefixUnaryExpression:
return emitPrefixUnaryExpression(<PrefixUnaryExpression>node);
case SyntaxKind.PostfixUnaryExpression:
return emitPostfixUnaryExpression(<PostfixUnaryExpression>node);
case SyntaxKind.BinaryExpression:
return emitBinaryExpression(<BinaryExpression>node);
case SyntaxKind.ConditionalExpression:
return emitConditionalExpression(<ConditionalExpression>node);
case SyntaxKind.SpreadElementExpression:
return emitSpreadElementExpression(<SpreadElementExpression>node);
case SyntaxKind.YieldExpression:
return emitYieldExpression(<YieldExpression>node);
case SyntaxKind.OmittedExpression:
return;
case SyntaxKind.Block:
case SyntaxKind.ModuleBlock:
return emitBlock(<Block>node);
case SyntaxKind.VariableStatement:
return emitVariableStatement(<VariableStatement>node);
case SyntaxKind.EmptyStatement:
return write(";");
case SyntaxKind.ExpressionStatement:
return emitExpressionStatement(<ExpressionStatement>node);
case SyntaxKind.IfStatement:
return emitIfStatement(<IfStatement>node);
case SyntaxKind.DoStatement:
return emitDoStatement(<DoStatement>node);
case SyntaxKind.WhileStatement:
return emitWhileStatement(<WhileStatement>node);
case SyntaxKind.ForStatement:
return emitForStatement(<ForStatement>node);
case SyntaxKind.ForOfStatement:
case SyntaxKind.ForInStatement:
return emitForInOrForOfStatement(<ForInStatement>node);
case SyntaxKind.ContinueStatement:
case SyntaxKind.BreakStatement:
return emitBreakOrContinueStatement(<BreakOrContinueStatement>node);
case SyntaxKind.ReturnStatement:
return emitReturnStatement(<ReturnStatement>node);
case SyntaxKind.WithStatement:
return emitWithStatement(<WithStatement>node);
case SyntaxKind.SwitchStatement:
return emitSwitchStatement(<SwitchStatement>node);
case SyntaxKind.CaseClause:
case SyntaxKind.DefaultClause:
return emitCaseOrDefaultClause(<CaseOrDefaultClause>node);
case SyntaxKind.LabeledStatement:
return emitLabelledStatement(<LabeledStatement>node);
case SyntaxKind.ThrowStatement:
return emitThrowStatement(<ThrowStatement>node);
case SyntaxKind.TryStatement:
return emitTryStatement(<TryStatement>node);
case SyntaxKind.CatchClause:
return emitCatchClause(<CatchClause>node);
case SyntaxKind.DebuggerStatement:
return emitDebuggerStatement(node);
case SyntaxKind.VariableDeclaration:
return emitVariableDeclaration(<VariableDeclaration>node);
case SyntaxKind.ClassExpression:
return emitClassExpression(<ClassExpression>node);
case SyntaxKind.ClassDeclaration:
return emitClassDeclaration(<ClassDeclaration>node);
case SyntaxKind.InterfaceDeclaration:
return emitInterfaceDeclaration(<InterfaceDeclaration>node);
case SyntaxKind.EnumDeclaration:
return emitEnumDeclaration(<EnumDeclaration>node);
case SyntaxKind.EnumMember:
return emitEnumMember(<EnumMember>node);
case SyntaxKind.ModuleDeclaration:
return emitModuleDeclaration(<ModuleDeclaration>node);
case SyntaxKind.ImportDeclaration:
return emitImportDeclaration(<ImportDeclaration>node);
case SyntaxKind.ImportEqualsDeclaration:
return emitImportEqualsDeclaration(<ImportEqualsDeclaration>node);
case SyntaxKind.ExportDeclaration:
return emitExportDeclaration(<ExportDeclaration>node);
case SyntaxKind.ExportAssignment:
return emitExportAssignment(<ExportAssignment>node);
case SyntaxKind.SourceFile:
return emitSourceFileNode(<SourceFile>node);
}
}

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

function emitFunctionDeclaration(node: FunctionLikeDeclaration) {
if (nodeIsMissing(node.body)) {
return emitOnlyPinnedOrTripleSlashComments(node);
}
if (node.kind !== SyntaxKind.MethodDeclaration && node.kind !== SyntaxKind.MethodSignature) {
// Methods will emit the comments as part of emitting method declaration
emitLeadingComments(node);
}
// For targeting below es6, emit functions-like declaration including arrow function using function keyword.
// When targeting ES6, emit arrow function natively in ES6 by omitting function keyword and using fat arrow instead
if (!shouldEmitAsArrowFunction(node)) {
if (isES6ExportedDeclaration(node)) {
write("export ");
if (node.flags & NodeFlags.Default) {
write("default ");
}
}
write("function");
if (languageVersion >= ScriptTarget.ES6 && node.asteriskToken) {
write("*");
}
write(" ");
}
if (shouldEmitFunctionName(node)) {
emitDeclarationName(node);
}
emitSignatureAndBody(node);
if (languageVersion < ScriptTarget.ES6 && node.kind === SyntaxKind.FunctionDeclaration && node.parent === currentSourceFile && node.name) {
emitExportMemberAssignments((<FunctionDeclaration>node).name);
}
if (node.kind !== SyntaxKind.MethodDeclaration && node.kind !== SyntaxKind.MethodSignature) {
emitTrailingComments(node);
}
}