vue-element-admin项目使用Export2Excel导出excel样式修改，复杂表头

主要是在vue-element-admin自带Export2Excel模板的基础上进行修改，进行单元格宽度，边框，字体，颜色等设置以及复杂表头的处理

参考链接: https://www.cnblogs.com/yinxingen/p/11052184.html.

1. 安装xlsx-style:npm install --save xlsx-style，
import XLSX from "xlsx-style"报错：This relative module was not found: ./cptable in ./node_modules/xlsx-style@0.8.13@xlsx-style/dist/cpexcel.js，需要修改源码：
在 \node_modules\xlsx-style\dist\cpexcel.js找到 var cpt = require(’./cpt’ + ‘able’); 并改成 var cpt = cptable;

2. 本地src/vendor/Export2Excel.js 文件修改

import { saveAs } from "file-saver";
// import XLSX from "xlsx";
import XLSX from "xlsx-style";

function generateArray(table) {
  var out = [];
  var rows = table.querySelectorAll("tr");
  var ranges = [];
  for (var R = 0; R < rows.length; ++R) {
    var outRow = [];
    var row = rows[R];
    var columns = row.querySelectorAll("td");
    for (var C = 0; C < columns.length; ++C) {
      var cell = columns[C];
      var colspan = cell.getAttribute("colspan");
      var rowspan = cell.getAttribute("rowspan");
      var cellValue = cell.innerText;
      if (cellValue !== "" && cellValue == +cellValue) cellValue = +cellValue;
      
      //Skip ranges
      ranges.forEach(function (range) {
        if (
          R >= range.s.r &&
          R <= range.e.r &&
          outRow.length >= range.s.c &&
          outRow.length <= range.e.c
        ) {
          for (var i = 0; i <= range.e.c - range.s.c; ++i) outRow.push(null);
        }
      });

      //Handle Row Span
      if (rowspan || colspan) {
        rowspan = rowspan || 1;
        colspan = colspan || 1;
        ranges.push({
          s: {
            r: R,
            c: outRow.length
          },
          e: {
            r: R + rowspan - 1,
            c: outRow.length + colspan - 1
          }
        });
      }

      //Handle Value
      outRow.push(cellValue !== "" ? cellValue : null);

      //Handle Colspan
      if (colspan)
        for (var k = 0; k < colspan - 1; ++k) outRow.push(null);
    }
    out.push(outRow);
  }
  return [out, ranges];
}

function datenum(v, date1904) {
  if (date1904) v += 1462;
  var epoch = Date.parse(v);
  return (epoch - new Date(Date.UTC(1899, 11, 30))) / (24 * 60 * 60 * 1000);
}

function sheet_from_array_of_arrays(data, opts) {
  var ws = {};
  var range = {
    s: {
      c: 10000000,
      r: 10000000
    },
    e: {
      c: 0,
      r: 0
    }
  };
  for (var R = 0; R != data.length; ++R) {
    for (var C = 0; C != data[R].length; ++C) {
      if (range.s.r > R) range.s.r = R;
      if (range.s.c > C) range.s.c = C;
      if (range.e.r < R) range.e.r = R;
      if (range.e.c < C) range.e.c = C;
      var cell = {
        v: data[R][C]
      };
      // 如果单元格所在的值为空，让其值为“——”，否则下面设置的边框对其不生效
      if (cell.v == null) {
        cell.v = "——";
      }
      var cell_ref = XLSX.utils.encode_cell({
        c: C,
        r: R
      });

      if (typeof cell.v === "number") cell.t = "n";
      else if (typeof cell.v === "boolean") cell.t = "b";
      else if (cell.v instanceof Date) {
        cell.t = "n";
        cell.z = XLSX.SSF._table[14];
        cell.v = datenum(cell.v);
      } else cell.t = "s";

      ws[cell_ref] = cell;
    }
  }
  if (range.s.c < 10000000) ws["!ref"] = XLSX.utils.encode_range(range);
  return ws;
}

function Workbook() {
  if (!(this instanceof Workbook)) return new Workbook();
  this.SheetNames = [];
  this.Sheets = {};
}

function s2ab(s) {
  var buf = new ArrayBuffer(s.length);
  var view = new Uint8Array(buf);
  for (var i = 0; i != s.length; ++i) view[i] = s.charCodeAt(i) & 0xff;
  return buf;
}

export function export_table_to_excel(id) {
  var theTable = document.getElementById(id);
  var oo = generateArray(theTable);
  var ranges = oo[1];

  /* original data */
  var data = oo[0];
  var ws_name = "SheetJS";

  var wb = new Workbook(),
    ws = sheet_from_array_of_arrays(data);

  /* add ranges to worksheet */
  // ws['!cols'] = ['apple', 'banan'];
  ws["!merges"] = ranges;

  /* add worksheet to workbook */
  wb.SheetNames.push(ws_name);
  wb.Sheets[ws_name] = ws;

  var wbout = XLSX.write(wb, {
    bookType: "xlsx",
    bookSST: false,
    type: "binary"
  });

  saveAs(
    new Blob([s2ab(wbout)], {
      type: "application/octet-stream"
    }),
    "test.xlsx"
  );
}
// 主要修改内容在这里
export function export_json_to_excel({
  title, // 新增的参数，表格标题
  multiHeader = [],
  header,
  data,
  filename,
  merges = [],
  autoWidth = true,
  bookType = "xlsx"
} = {}) {
  /* original data */
  filename = filename || "excel-list";
  data = [...data];
  data.unshift(header);
  for (let i = multiHeader.length - 1; i > -1; i--) {
    data.unshift(multiHeader[i]);
  }
  data.unshift(title); // 表格标题
  var ws_name = "SheetJS";
  var wb = new Workbook(),
    ws = sheet_from_array_of_arrays(data);

  if (merges.length > 0) {
    if (!ws["!merges"]) ws["!merges"] = [];
    merges.forEach(item => {
      ws["!merges"].push(XLSX.utils.decode_range(item));
    });
  }

// 设置单元格宽度
  if (autoWidth) {
    /*设置worksheet每列的最大宽度*/
    const colWidth = data.map(row =>
      row.map(val => {
        /*先判断是否为null/undefined*/
        if (val == null || val == undefined) {
          return {
            wch: 10
          };
        } else if (val.toString().charCodeAt(0) > 255) {
          /*再判断是否为中文*/
          return {
            wch: val.toString().length * 2
          };
        } else {
          return {
            wch: val.toString().length * 1.5
          };
        }
      })
    );
    /*以主表第二行为初始值，因为我的第一行是表格标题，会比较长，所以以主表第二行为初始值*/
    let result = colWidth[1];
    for (let i = 1; i < colWidth.length; i++) {
      for (let j = 0; j < colWidth[i].length; j++) {
        if (result[j]["wch"] < colWidth[i][j]["wch"]) {
          result[j]["wch"] = colWidth[i][j]["wch"];
        }
      }
    }
    ws["!cols"] = result;
  }
  /* add worksheet to workbook */
  wb.SheetNames.push(ws_name);
  wb.Sheets[ws_name] = ws;

  var dataInfo = wb.Sheets[wb.SheetNames[0]];
    // 设置单元格框线
  const borderAll = {
    top: {
      style: "thin"
    },
    bottom: {
      style: "thin"
    },
    left: {
      style: "thin"
    },
    right: {
      style: "thin"
    }
  };
  
  // 给所有单元格加上边框，内容居中，字体，字号，标题表头特殊格式部分后面替换
  for (var i in dataInfo) {
    if (
      i == "!ref" ||
      i == "!merges" ||
      i == "!cols" ||
      i == "!rows" ||
      i == "A1"
    ) { } else {
      dataInfo[i + ""].s = {
        border: borderAll,
        alignment: {
          horizontal: "center",
          vertical: "center"
        },
        font: {
          name: "微软雅黑",
          sz: 10
        }
      };
    }
  }
  
  // 设置表格样式
  const arrabc = ["A",
    "B",
    "C",
    "D",
    "E",
    "F",
    "G",
    "H",
    "I",
    "J",
    "K",
    "L",
    "M",
    "N",
    "O",
    "P",
    "Q",
    "R",
    "S",
    "T",
    "U",
    "V",
    "W",
    "X",
    "Y",
    "Z"
  ]
  
  // 给标题、表格描述信息、表头等部分加上特殊格式
  arrabc.some(function (v) {
    for (let j = 1; j < multiHeader.length + 3; j++) {
      const _v = v + j
      if (dataInfo[_v]) {
        dataInfo[_v].s = {};
        // 标题部分A1-Z1
        if (j == 1) {
          dataInfo[v + j].s = {
            font: {
              name: "微软雅黑",
              sz: 12,
              color: {
                rgb: "000000"
              },
              bold: true,
              italic: false,
              underline: false
            },
            alignment: {
              horizontal: "center",
              vertical: "center"
            }
          };
        } else {
        // 表头部分,根据表头特殊格式设置
          if (multiHeader.length == 0) {
          // multiHeader.length = 0 时表头没有合并单元格，表头只占1行A2-Z2
            const fv = v + (multiHeader.length + 2)
            dataInfo[fv].s = {
              border: borderAll,
              font: {
                name: "微软雅黑",
                sz: 11,
                bold: true
              },
              alignment: {
                horizontal: "center",
                vertical: "center"
              },
              fill: {
                fgColor: {
                  rgb: "f0f0f0"
                },
              },
            }
          } else if (multiHeader.length == 1) {
          // multiHeader.length = 0 时表头有合并单元格，表头只占2行A2-Z2，A3-Z3，这是没有描述信息只有表头合并的
            dataInfo[v + j].s = {
              border: borderAll,
              font: {
                name: "微软雅黑",
                sz: 11,
              },
              alignment: {
                horizontal: "center",
                vertical: "center"
              },
              fill: {
                fgColor: {
                  rgb: "f0f0f0"
                }
              },
            }
          } else {
           // multiHeader.length = 0 时表头有合并单元格，表头多行
            dataInfo[v + j].s = {
              border: borderAll,
              font: {
                name: "微软雅黑",
                sz: 9,
              },
              alignment: {
                horizontal: "left",
                vertical: "center"
              }
            }
          }
        }
        // multiHeader.length + 2 是表头的最后1行
        dataInfo[v + (multiHeader.length + 2)].s = {
          border: borderAll,
          font: {
            name: "微软雅黑",
            sz: 10,
          },
          alignment: {
            horizontal: "center",
            vertical: "center"
          },
          fill: {
            fgColor: {
              rgb: "f0f0f0"
            }
          },
        }
      }
    }
  });
  
  var wbout = XLSX.write(wb, {
    bookType: bookType,
    bookSST: false,
    type: "binary"
  });
  saveAs(
    new Blob([s2ab(wbout)], {
      type: "application/octet-stream"
    }),
    `${filename}.${bookType}`
  );
}

3. 调用Export2Excel.js，根据实际需要给 title, multiHeader header, data,merges 等参数赋值，复杂多级表头主要在multiHeader 处理，multiHeader 是数组，可以添加多个数组

// 调用
handleDownload() {
      import("@/vendor/Export2Excel").then(excel => {
        const title = [this.title, "", ""];
        const header = ["序号", "***", "***"];
        const filterVal = ["index", "***", "***"];
        const merges = ["A1:C1"];
        const query = {
          pageNum: 1,
          pageSize: this.total
        };
        getData(query).then(res => {
          const list = res.data.list;
          const data = this.formatJson(filterVal, list);
          excel.export_json_to_excel({
            title,
            header,
            merges,
            data,
            filename: this.title,
            autoWidth: this.autoWidth,
            bookType: this.bookType
          });
        });
      });
    },
    formatJson(filterVal, jsonData) {
      jsonData.map((row, index) => {
        row.index = index + 1;
      });
      return jsonData.map(v =>
        filterVal.map(j => {
          return v[j];
        })
      );
    }
  },

// 多级表头
const multiHeader = [
          ["title", "", "", "", "", "", "", ""],
          [
            "日期",
            this.time,
            "**",
            "**",
            "**",
            "**",
            "**",
            "**",
          ],
          [
            "联系人",
            "张三",
            "**",
            "**",
            "联系电话",
            "123456789*",
            "**",
            "**",
          ]
        ];

tip: 这里表头部分如果不能满足所有表格，可以根据实际需要拷贝多个Export2Excel.js文件调整表头部分，根据实际需要引入不同的Export2Excel.js文件