写在前面：这是纯前端导出，导出的表格是二级表头，内容是四级单元格（单元格内有四小格），这几个点学会之后应该能适应大部分导出excel的需求了。本次功能记录真实有效。对于之前没接触过导出excel需求的小伙伴可能会有一点点的难度，希望各位能静下心来阅读和学习。有什么问题请在下方留言，我会尽力解答~

导出excel的前提是我们需要加载以下框架or文件

• vue + elementui（表格是用这个ui框架写的）
• Export2Excel.js
• Blob.js
• xlsx-style（npm install --save xlsx-style 这个插件用来设置表头文字水平垂直居中）

我先附上效果图，各位看一下是否符合自己的需求

以下是正文部分

首先是在项目中加入Export2Excel.js文件。该文件与官网的不同，官网的好像只能单表头导出excel。为了满足二级表头导出excel，并且需要设置表头的样式，所以我改了源码。主要是新增并暴露出去一个方法（ export_json_to_excel2 ），在这个方法内部还新增了表头样式的修改。该方法用来实现二级表头导出的功能。方法的参数在源码内部有说明。

第八行导入了一个xlsx-style插件，所以需要npm安装一下（ npm install --save xlsx-style ）。安装这个插件之后可能会有一个问题。控制台报异常：This relative module was not found: ./cptable in ./node_modules/xlsx-style@0.8.13@xlsx-style/dist/cpexcel.js。
可以直接修改这个插件的源码：在\node_modules\xlsx-style\dist\cpexcel.js 807行 的 var cpt = require(’./cpt’ + ‘able’); 改成 var cpt = cptable;

//Export2Excel.js
/* eslint-disable */
require('script-loader!file-saver');
//路径是您存放Blob.js的路径
require('script-loader!@/vendor/Blob');
/* eslint-disable */
// 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]
      };
      if (cell.v == null) continue;
      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")
}
//单表头导出excel
export function export_json_to_excel(th, jsonData, defaultTitle) {
  /* original data */
  var data = jsonData;
  console.log('th',th);
  console.log('jsonData',jsonData);
  console.log('defaultTitle',defaultTitle)
  data.unshift(th);
  var ws_name = "SheetJS";
  var wb = new Workbook(), ws = sheet_from_array_of_arrays(data);
  /*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) {
    return {'wch': 10};
  }
  /*再判断是否为中文*/
else if (val.toString().charCodeAt(0) > 255) {
    return {'wch': val.toString().length * 2};
  } else {
    return {'wch': val.toString().length};
  }
}))
  /*以第一行为初始值*/
  let result = colWidth[0];
  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 wbout = XLSX.write(wb, {bookType: 'xlsx', bookSST: false, type: 'binary'});
  var title = defaultTitle || 'excel-list'
  saveAs(new Blob([s2ab(wbout)], {type: "application/octet-stream"}), title + ".xlsx")
}

//二级表头导出excel
/**
 * multiHeader: 一级表头
 * header: 二级表头
 * data: 表格的数据
 * filename: 导出的文件名称
 * headerStyle: 表头样式
 * merges: 需要合并的每个单元格(不仅能合并表头单元格，还能合并表格内容单元格)
 * autoWidth: excel中每个单元格是否自动宽度(这个参数默认为true，而且也不建议设置为false，因为这将导致excel可读性非常差劲！)
 * bookType: 文件类型
 * @param {*} param0 
 */
export function export_json_to_excel2({
  multiHeader = [],
  header,
  data,
  filename,
  headerStyle = [],
  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])
  }

  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))
    })
  }

  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) {
        return {
          'wch': 10
        };
      }
      /*再判断是否为中文*/
      else if (val.toString().charCodeAt(0) > 255) {
        return {
          'wch': val.toString().length * 2
        };
      } else {
        return {
          'wch': val.toString().length
        };
      }
    }))
    /*以第一行为初始值*/
    let result = colWidth[0];
    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]];
  
  /**
   * tableTitleFont: 用来存储表头的样式
   * border: 表头的边框样式
   * font: 表头的文字样式
   * alignment: 表头文字的空间设置(这里是设置水平垂直居中)
   * fill: 表头的单元格颜色填充(背景色)
   */
  var tableTitleFont = {
    // border: {
    //   top: {
    //     style: 'thin',
    //     color: {rgb: "ffffff"},
    //   },
    //   right: {
    //     style: 'thin',
    //     color: {rgb: "ffffff"},
    //   },
    //   bottom: {
    //     style: 'thin',
    //     color: {rgb: "ffffff"},
    //   },
    //   left: {
    //     style: 'thin',
    //     color: {rgb: "ffffff"},
    //   },
    // },
    // font: {
    //   sz: 12,
    //   color: {rgb: "ffffff"},
    //   bold: true,
    // },
    alignment: {
      horizontal: "center",
      vertical: "center"
    },
    // fill: {
    //   fgColor: {rgb: "6495ED"},
    // },
  };

  for (var i = 0; i < headerStyle.length; i++) {
    dataInfo[headerStyle[i]].s = tableTitleFont;
  }
  var wbout = XLSX.write(wb, {
    bookType: bookType,
    bookSST: false,
    type: 'binary'
  });
  saveAs(new Blob([s2ab(wbout)], {
    type: "application/octet-stream"
  }), `${filename}.${bookType}`);
}

加入Blob.js文件，源码放在下方（不做修改，和官网的一样）

/* eslint-disable */
/* Blob.js
 * A Blob implementation.
 * 2014-05-27
 *
 * By Eli Grey, http://eligrey.com
 * By Devin Samarin, https://github.com/eboyjr
 * License: X11/MIT
 *   See LICENSE.md
 */
/*global self, unescape */
/*jslint bitwise: true, regexp: true, confusion: true, es5: true, vars: true, white: true,
 plusplus: true */
/*! @source http://purl.eligrey.com/github/Blob.js/blob/master/Blob.js */
(function (view) {
  "use strict";
  view.URL = view.URL || view.webkitURL;
  if (view.Blob && view.URL) {
    try {
      new Blob;
      return;
    } catch (e) {}
  }
  // Internally we use a BlobBuilder implementation to base Blob off of
  // in order to support older browsers that only have BlobBuilder
  var BlobBuilder = view.BlobBuilder || view.WebKitBlobBuilder || view.MozBlobBuilder || (function(view) {
    var
      get_class = function(object) {
        return Object.prototype.toString.call(object).match(/^\[object\s(.*)\]$/)[1];
      }
      , FakeBlobBuilder = function BlobBuilder() {
        this.data = [];
      }
      , FakeBlob = function Blob(data, type, encoding) {
        this.data = data;
        this.size = data.length;
        this.type = type;
        this.encoding = encoding;
      }
      , FBB_proto = FakeBlobBuilder.prototype
      , FB_proto = FakeBlob.prototype
      , FileReaderSync = view.FileReaderSync
      , FileException = function(type) {
        this.code = this[this.name = type];
      }
      , file_ex_codes = (
        "NOT_FOUND_ERR SECURITY_ERR ABORT_ERR NOT_READABLE_ERR ENCODING_ERR "
        + "NO_MODIFICATION_ALLOWED_ERR INVALID_STATE_ERR SYNTAX_ERR"
      ).split(" ")
      , file_ex_code = file_ex_codes.length
      , real_URL = view.URL || view.webkitURL || view
      , real_create_object_URL = real_URL.createObjectURL
      , real_revoke_object_URL = real_URL.revokeObjectURL
      , URL = real_URL
      , btoa = view.btoa
      , atob = view.atob
      , ArrayBuffer = view.ArrayBuffer
      , Uint8Array = view.Uint8Array
    ;
    FakeBlob.fake = FB_proto.fake = true;
    while (file_ex_code--) {
      FileException.prototype[file_ex_codes[file_ex_code]] = file_ex_code + 1;
    }
    if (!real_URL.createObjectURL) {
      URL = view.URL = {};
    }
    URL.createObjectURL = function(blob) {
      var
        type = blob.type
        , data_URI_header
      ;
      if (type === null) {
        type = "application/octet-stream";
      }
      if (blob instanceof FakeBlob) {
        data_URI_header = "data:" + type;
        if (blob.encoding === "base64") {
          return data_URI_header + ";base64," + blob.data;
        } else if (blob.encoding === "URI") {
          return data_URI_header + "," + decodeURIComponent(blob.data);
        } if (btoa) {
          return data_URI_header + ";base64," + btoa(blob.data);
        } else {
          return data_URI_header + "," + encodeURIComponent(blob.data);
        }
      } else if (real_create_object_URL) {
        return real_create_object_URL.call(real_URL, blob);
      }
    };
    URL.revokeObjectURL = function(object_URL) {
      if (object_URL.substring(0, 5) !== "data:" && real_revoke_object_URL) {
        real_revoke_object_URL.call(real_URL, object_URL);
      }
    };
    FBB_proto.append = function(data/*, endings*/) {
      var bb = this.data;
      // decode data to a binary string
      if (Uint8Array && (data instanceof ArrayBuffer || data instanceof Uint8Array)) {
        var
          str = ""
          , buf = new Uint8Array(data)
          , i = 0
          , buf_len = buf.length
        ;
        for (; i < buf_len; i++) {
          str += String.fromCharCode(buf[i]);
        }
        bb.push(str);
      } else if (get_class(data) === "Blob" || get_class(data) === "File") {
        if (FileReaderSync) {
          var fr = new FileReaderSync;
          bb.push(fr.readAsBinaryString(data));
        } else {
          // async FileReader won't work as BlobBuilder is sync
          throw new FileException("NOT_READABLE_ERR");
        }
      } else if (data instanceof FakeBlob) {
        if (data.encoding === "base64" && atob) {
          bb.push(atob(data.data));
        } else if (data.encoding === "URI") {
          bb.push(decodeURIComponent(data.data));
        } else if (data.encoding === "raw") {
          bb.push(data.data);
        }
      } else {
        if (typeof data !== "string") {
          data += ""; // convert unsupported types to strings
        }
        // decode UTF-16 to binary string
        bb.push(unescape(encodeURIComponent(data)));
      }
    };
    FBB_proto.getBlob = function(type) {
      if (!arguments.length) {
        type = null;
      }
      return new FakeBlob(this.data.join(""), type, "raw");
    };
    FBB_proto.toString = function() {
      return "[object BlobBuilder]";
    };
    FB_proto.slice = function(start, end, type) {
      var args = arguments.length;
      if (args < 3) {
        type = null;
      }
      return new FakeBlob(
        this.data.slice(start, args > 1 ? end : this.data.length)
        , type
        , this.encoding
      );
    };
    FB_proto.toString = function() {
      return "[object Blob]";
    };
    FB_proto.close = function() {
      this.size = this.data.length = 0;
    };
    return FakeBlobBuilder;
  }(view));
  view.Blob = function Blob(blobParts, options) {
    var type = options ? (options.type || "") : "";
    var builder = new BlobBuilder();
    if (blobParts) {
      for (var i = 0, len = blobParts.length; i < len; i++) {
        builder.append(blobParts[i]);
      }
    }
    return builder.getBlob(type);
  };
}(typeof self !== "undefined" && self || typeof window !== "undefined" && window || this.content || this));

调用二级表头导出excel的方法如下。我这个表格全是动态数据，需要调接口重组数据，代码太多，全是操作数组or对象，这些就略过啦。所以我只写出来这些参数的格式，方便大家查看是怎么调用导出方法的。下面我放一张截图，说明一下各个参数内部存放的数据是哪些~

import("@/excel/Export2Excel").then((excel) => {
    const multiHeader = [[]]  //一级表头
    const header = []	//二级表头
    const filterVal = []	//表头字段
    const list = [{}]	//表格内容数据
    const merges = []	//需要合并的单元格 -> A1:A2
    const data = this.formatJson(filterVal, list) //这个不管...调方法传参就行
    //这里还是使用export_json_to_excel方法比较好，方便操作数据
    const headerStyle  = []		//表头样式
    excel.export_json_to_excel2({
         multiHeader,
         header,
         data,
         filename: "交货计划表",
         headerStyle,
         merges
    });
});

调用导出方法里面用到一个函数，我放在下面，大家记得添加一下。

formatJson(filterVal, jsonData) {
    //console.log(filterVal, jsonData);
    return jsonData.map((v) =>
        filterVal.map((j) => {
            return v[j]
        })
    )
}