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.

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

emitJavaScriptWorker

The complete function:

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

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