app/node_modules/markdown-it-imsize/lib/helpers/parse_image_size.js

// Parse image size
//
'use strict';

function parseNextNumber(str, pos, max) {
  var code,
  start = pos,
  result = {
    ok: false,
    pos: pos,
    value: ''
  };

  code = str.charCodeAt(pos);

  while (pos < max && (code >= 0x30 /* 0 */ && code <= 0x39 /* 9 */) || code === 0x25 /* % */) {
    code = str.charCodeAt(++pos);
  }

  result.ok = true;
  result.pos = pos;
  result.value = str.slice(start, pos);

  return result;
}

module.exports = function parseImageSize(str, pos, max) {
  var code,
  result = {
    ok: false,
    pos: 0,
    width: '',
    height: ''
  };

  if (pos >= max) { return result; }

  code = str.charCodeAt(pos);

  if (code !== 0x3d /* = */) { return result; }

  pos++;

  // size must follow = without any white spaces as follows
  // (1) =300x200
  // (2) =300x
  // (3) =x200
  code = str.charCodeAt(pos);
  if (code !== 0x78 /* x */ && (code < 0x30 || code  > 0x39) /* [0-9] */) {
    return result;
  }

  // parse width
  var resultW = parseNextNumber(str, pos, max);
  pos = resultW.pos;

  // next charactor must be 'x'
  code = str.charCodeAt(pos);
  if (code !== 0x78 /* x */) { return result; }

  pos++;

  // parse height
  var resultH = parseNextNumber(str, pos, max);
  pos = resultH.pos;

  result.width = resultW.value;
  result.height = resultH.value;
  result.pos = pos;
  result.ok = true;
  return result;
};