getLinesAroundOffset.js

getLinesAroundOffset.js

/**
 * Gets the line at given offset in s, as well as `nLines` lines below and above.
 * If a line is very long (e.g. in bundled/obfuscated files), i.e. if it exceeds `maxChars`, get at most `maxChars` more in each direction
 */
function getLinesAroundOffset(s, offset, nLines = 1, maxChars = 200) {
  let start = offset - 1;
  for (let i = 0; i < nLines; ++i) {
    const newIdx = s.lastIndexOf('\n', start) - 1;
    if (Math.abs(start - newIdx) > maxChars) {
      // probably compressed code
      start -= maxChars;
      break;
    }
    if (newIdx >= 0) {
      start = newIdx;
    }
  }
  let end = offset + 1;
  for (let i = 0; i <= nLines; ++i) {
    const newIdx = s.indexOf('\n', end) + 1;
    if (Math.abs(end - newIdx) > maxChars) {
      // probably compressed code
      end += maxChars;
      break;
    }
    if (newIdx >= 0) {
      end = newIdx;
    }
  }

  return s.substring(start, end);
}