Formatting printed code with TypeScript compiler API

Question

I have a TypeScript code generation scenario, where I construct an AST and then print it and save to a file. The printed class declaration elements, for example, are clustered together. How could one achieve the type of pretty printing that would insert newlines after new method/constructor declarations and perhaps could stack extension methods in new lines?

private baseUrl = "api/students";
constructor(private http: Http) { }
list(): Promise<Student[]> {
    return this.http.get(this.baseUrl + "/").toPromise().then((response: Response) => response.json()).catch(this.handleError);
}
get(id: number): Promise<Student> {
    return this.http.get(this.baseUrl + ("/" + id)).toPromise().then((response: Response) => response.json()).catch(this.handleError);
}

Any existing API`s can suffice or is there a way to manually insert some trailing trivia after declarations?

How do you generate this file? I think you can insert white characters into AST. See ts.SyntaxKind.NewLineTrivia and ts.SyntaxKind.WhitespaceTrivia — Misaz
– Misaz, Commented Jul 24, 2017 at 5:55

David Sherret · Accepted Answer · 2017-12-08 02:24:36Z

The formatting API will help with this:

const languageService: ts.LanguageService = ...;
const sourceFile: ts.SourceFile = ...;
const filePath: string = ...;

const textChanges = languageService.getFormattingEditsForDocument(filePath, {
    convertTabsToSpaces: true,
    insertSpaceAfterCommaDelimiter: true,
    insertSpaceAfterKeywordsInControlFlowStatements: true,
    insertSpaceBeforeAndAfterBinaryOperators: true,
    newLineCharacter: "\n",
    indentStyle: ts.IndentStyle.Smart,
    indentSize: 4,
    tabSize: 4
});

let finalText = sourceFile.getFullText();

for (const textChange in textChanges.sort((a, b) => b.span.start - a.span.start)) {
    const {span} = textChange;
    finalText = finalText.slice(0, span.start) + textChange.newText
        + finalText.slice(span.start + span.length);
}

// finalText contains the formatted text

That said, you might want to check out tsfmt which will do this for you.

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