Is it possible to insert a comment after a value?

[blhoward2]

After a json has been parsed, is it possible to insert a new comment that will then be retained? If so, how? I'm pulling my hair out...

[psulek]

I am also curious about this. Also i want to know how to add comments when building json object at runtime (not loading/parsing).

So for example i have this code:

const {stringify} = require('comment-json');
let obj = { name: "peter"; age: 20; };
// TODO: how to add comment before property "name" here before calling stringify ?
const str = stringify(obj);

[psulek]

@blhoward2 @kaelzhang I found a wacky way to do this (ugly but working):

obj[Symbol.for('before:name')] = [{type: 'LineComment', inline: false, value: 'my custom comment'}];

will stringify to:

{ 
  // my custom comment
  name: "peter"; 
  age: 20; 
};

[HanYangZhao]

I have a similar use case but the comment i wanted for entries in a list

I have this

{
    "members": [
        "user1", // comment
        "user2"  // comment2
    ]
}

And I want to have this

{
    "members": [
        "user1",   // comment
        "user2",  // comment2
        "user3"  // comment3
    ]
}

I wrote the following code

const {
  parse,
  stringify
} = require('comment-json')
const fs = require('fs')
const { inspect } = require('util')

const findMembersLineNumber = (filePath, groupName) => {
  const fileContent = fs.readFileSync(filePath, { encoding: 'utf-8' })
  const lines = fileContent.split(/\r?\n/)
  let isWithinTargetBlock = false

  for (let i = 0; i < lines.length; i++) {
    const line = lines[i]
    if (line.includes(`"${groupName}"`)) {
      isWithinTargetBlock = true
    }
    if (isWithinTargetBlock && line.includes('"members"')) {
      const leadingWhitespace = line.match(/^\s*/)[0]
      const whitespaceCount = leadingWhitespace.length
      // console.log(`Number of leading whitespace characters: ${whitespaceCount}`)
      // console.log(`Line number of "members" under "${groupName}": ${i + 1}`)
      return { lineNumber: i + 1, whitespaceCount }
    }
  }
}
const appendMember = (obj, valueToAdd = null, comment = null, lineNumberObj) => {
  if (valueToAdd) {
    const members = obj.members
    const memberKey = 'after:' + (members.length)
    const newSymbol = Symbol(memberKey)
    members.push(valueToAdd)
    members[newSymbol] = [
      {
        type: 'LineComment',
        value: comment,
        loc: {
          start: { line: lineNumberObj.lineNumber + members.length, column: lineNumberObj.whitespaceCount + 3 + valueToAdd.length + 5 },
          end: { line: lineNumberObj.lineNumber + members.length, column: lineNumberObj.whitespaceCount + 3 + valueToAdd.length + 5 + comment.length + 2 }
        },
        inline: true
      }
    ]
  }
  return obj
}

parse(fs.readFileSync('test.jsonc').toString(), null, true)
const obj = parse(fs.readFileSync('test.jsonc').toString())
const startingLineNumber = findMembersLineNumber('test.jsonc', 'members')
const modifiedObj = appendMember(obj, 'user3', ' comment3', startingLineNumber)

const hidden = (
  inspect(modifiedObj, {
    showHidden: true,
    depth: 10
  })
)
console.log(hidden)
const output = stringify(modifiedObj, null, 2)
console.log(output)

I used util.inspect to looks at the object, which looked correct to me.

{
  members: CommentArray(3) [
    'user1',
    'user2',
    'user3',
    [length]: 3,
    [Symbol(after:0)]: [
      {
        type: 'LineComment',
        value: ' comment',
        loc: {
          start: { line: 3, column: 17 },
          end: { line: 3, column: 27 }
        },
        inline: true
      },
      [length]: 1
    ],
    [Symbol(after:1)]: [
      {
        type: 'LineComment',
        value: ' comment2',
        loc: {
          start: { line: 4, column: 17 },
          end: { line: 4, column: 28 }
        },
        inline: true
      },
      [length]: 1
    ],
    [Symbol(after:2)]: [
      {
        type: 'LineComment',
        value: ' comment3',
        loc: {
          start: { line: 5, column: 17 },
          end: { line: 5, column: 28 }
        },
        inline: true
      },
      [length]: 1
    ]
  ]
}

But the output from stringify didn't have the new comment.

{
  "members": [
    "user1", // comment
    "user2", // comment2
    "user3"
  ]
}