emitter-sourcemaps.md

Emitter SourceMaps

We said that the bulk of the emitter.ts is the local function emitJavaScript (we showed the initialization routine of this function before). It basically sets up a bunch of locals and hits off to emitSourceFile. The following is a revisiting of the function, this time focusing on SourceMap stuff:

function emitJavaScript(jsFilePath: string, root?: SourceFile) {

    // STUFF ........... removed

    let writeComment = writeCommentRange;

    /** Write emitted output to disk */
    let writeEmittedFiles = writeJavaScriptFile;

    /** 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

The imporant function call here : initializeEmitterWithSourceMaps which is a function local to emitJavaScript that overrides some locals that were already defined here. At the bottom of initializeEmitterWithSourceMaps you will notice the overriding:

    // end of `initializeEmitterWithSourceMaps`

    writeEmittedFiles = writeJavaScriptAndSourceMapFile;
    emit = emitNodeWithSourceMap;
    emitStart = recordEmitNodeStartSpan;
    emitEnd = recordEmitNodeEndSpan;
    emitToken = writeTextWithSpanRecord;
    scopeEmitStart = recordScopeNameOfNode;
    scopeEmitEnd = recordScopeNameEnd;
    writeComment = writeCommentRangeWithMap;

This means that the bulk of emitter code can not care about SourceMap and just use these local functions the same way with or without SourceMaps.