请问如何简化下面的代码？

功能描述

当 const mergeTable=[2]时，
函数返回
{ rowSpan: 2 }
{ rowSpan: 0 }

当 const mergeTable=[2,3]时,函数返回
{ rowSpan: 2 }
{ rowSpan: 0 }
{ rowSpan: 3 }
{ rowSpan: 0 }
{ rowSpan: 0 }

当const mergeTable=[2,3,3,2]函数返回
{ rowSpan: 2 }
{ rowSpan: 0 }
{ rowSpan: 3 }
{ rowSpan: 0 }
{ rowSpan: 0 }
{ rowSpan: 3 }
{ rowSpan: 0 }
{ rowSpan: 0 }
{ rowSpan: 2 }
{ rowSpan: 0 }

需要优化的函数

功能已经实现，代码冗余，请问如何优化

// const mergeTable=[2] // 测试 ok
const mergeTable = [2, 3]; // 测试ok
// const mergeTable=[2,3,3,2]; // 测试ok

// 如何简化这个函数
function renderRowSpan(index) {
  for (let i in mergeTable) {
      i=Number(i);
    if (i === 0) {
      if (index === 0) {
        return { rowSpan: mergeTable[0] };
      } else if (index < mergeTable[0]) {
        return { rowSpan: 0 };
      }
    }

    if (i === 1) {
      if (index === mergeTable[0]) {
        return { rowSpan: mergeTable[1] };
      }
      if (index < mergeTable[0] + mergeTable[1]) {
        return { rowSpan: 0 };
      }
    }

    if (i === 2) {
      if (index === mergeTable[0] + mergeTable[1]) {
        return { rowSpan: mergeTable[2] };
      }
      if (index < mergeTable[0] + mergeTable[1] + mergeTable[2]) {
        return { rowSpan: 0 };
      }
    }


      if (i === 3) {
          if (index === mergeTable[0] + mergeTable[1]+mergeTable[2]) {
              return { rowSpan: mergeTable[3] };
          }
          if (index < mergeTable[0] + mergeTable[1] + mergeTable[2]+ mergeTable[3]) {
              return { rowSpan: 0 };
          }
      }
  }
}

// 外部方法会渲染index
for (let index = 0; index < 10; index++) {
  console.log(renderRowSpan(index));
}