根据每个数组中的第一个值合并数组

const arrays = [
  [1, 'a', 'b'],
  [2, 'c', 'd'],
  [1, 'e', 'f'],
  [3, 'g', 'h'],
  [2, 'i', 'j']
];

const mergedArrays = arrays.reduce((acc, curr) => {
  const existingIndex = acc.findIndex(item => item[0] === curr[0]);
  if (existingIndex !== -1) {
    acc[existingIndex].push(...curr.slice(1));
  } else {
    acc.push([curr[0], ...curr.slice(1)]);
  }
  return acc;
}, []);

console.log(mergedArrays);

[
  [1, 'a', 'b', 'e', 'f'],
  [2, 'c', 'd', 'i', 'j'],
  [3, 'g', 'h']
]