Typescript AST factory - how to use comments?

user_1126273 0
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I have the following ast:

import { factory as f } from 'typescript'

const typeDeclaration = f.createTypeAliasDeclaration(
  [],
  [],
  'TestType',
  [],
  f.createTypeLiteralNode([
    f.createPropertySignature([], 'str', undefined, f.createKeywordTypeNode(SyntaxKind.StringKeyword)),
  ]),
)

Which represents:

type TestType = {
  str: string
}

How would I build an AST representing this code? Are comments even part of the AST?

/* Some comment on type */
type TestType = {
  /* Some comment on property */
  str: string
}

I have seen there are many methods available on the factory object for creating doc-comments, but I haven't found any examples on how to use them.

In case it's only possible in doc-comment format I'd be interested in examples for that too:

/** Some comment on type */
type TestType = {
  /** Some comment on property */
  str: string
}
typescript abstract-syntax-tree factory comments
1 Answers

Based on @AlexWayne's answer it seems you can wrap each Node into an addSyntheticLeadingComment call. You can then specify the raw text that goes between the /* and */ tokens.

const typeDeclWithComment = addSyntheticLeadingComment(
  typeDeclaration, // The node
  SyntaxKind.MultiLineCommentTrivia, // Node type
  'my comment', // the comment text between comment tokens
  true, // add a trailing newline after */
)

Which will result in something like this:

/*my comment*/
type TestType = {
  str: string
}

In case you want to do doc-comment style comments, you can do something like:

const typeDeclWithComment = addSyntheticLeadingComment(
  typeDeclaration,
  SyntaxKind.MultiLineCommentTrivia,
  '*\n * First line of doc-comment\n * second line of doc-comment\n ', 
  true, 
)

Which will be printed as:

/**
 * First line of doc-comment
 * second line of doc-comment
 */
type TestType = {
  str: string
}

But you are on your own with indentation.

user_11262730
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