lodash的basexor疑惑

Question

function baseXor(arrays, iteratee, comparator) {
  const length = arrays.length
  if (length < 2) {
    return length ? baseUniq(arrays[0]) : []
  }
  let index = -1
  const result = new Array(length)

  while (++index < length) {
    const array = arrays[index]
    let othIndex = -1

    while (++othIndex < length) {
      if (othIndex != index) {
        result[index] = baseDifference(result[index] || array, arrays[othIndex], iteratee, comparator)
      }
    }
  }
  return baseUniq(baseFlatten(result, 1), iteratee, comparator)
}

1.为什么用while不用for
2.为什么每次循环都从第一个开始比
就是为什么不用

for(let i=0;i<len;i++){
    for(let j=i;j<len;j++){}
}

然后两个数组一对比就得到不同都值
就是
[1,2],[2,3]->[1,3]
而不是用_deffirence那种方式
[1,2],[2,3]->[1]