prettierCursor.js

const prettier = require("prettier");
const chalk = require("chalk");

const normal = chalk.grey;
const highlight = chalk.white.bgBlue.bold;

function showNewline(s) {
  return s.replace(/\n/g, "\u23ce\n");
}

function printWithHighlight({ formatted, cursorOffset }) {
  process.stdout.write(
    normal(showNewline(formatted.substring(0, cursorOffset))) +
      highlight(
        showNewline(formatted.substring(cursorOffset, cursorOffset + 1))
      ) +
      normal(showNewline(formatted.substring(cursorOffset + 1))) +
      "\n"
  );
}

function showCursor(parser, code) {
  for (let cursorOffset = 0; cursorOffset < code.length; ++cursorOffset) {
    console.log(`--- cursorOffset ${cursorOffset}`);
    printWithHighlight({ formatted: code, cursorOffset });
    printWithHighlight(
      prettier.formatWithCursor(code, { parser, cursorOffset })
    );
  }
}

showCursor(
  "ruby",
  `
unless false
  true
end.to_s
`
);

/*
showCursor(
  "babel",
  `

function  foo ( x )  {
  return "bar" ;
  }
`
);
*/