Updated version

Spreadsheet.js

'use strict';

import FileSaver from 'file-saver';
import JSZip     from 'jszip';

class Spreadsheet {

  /**
   * Holds all replacement strings to escape
   *
   * @returns {Object<string>}
   */
  static get escapeReplacements () {
    return {
      '&':  '&amp',
      '<':  '&lt',
      '>':  '&gt',
      '"':  '&quot',
      '\'': '&#39'
    };
  }

  /**
   * Regex to test for unescaped HTML
   *
   * @returns {RegExp}
   */
  static get escapeRegex () {
    return /[&<>"']/g;
  }

  /**
   * Holds all error messages
   * @returns {{missing_key_filename: string, invalid_type_filename: string, invalid_type_sheet: string, invalid_type_sheet_data: string}}
   */
  static get errors () {
    return {
      missing_key_filename:    'zipclex config missing property filename',
      invalid_type_filename:   'zipclex filename can only be of type string',
      invalid_type_sheet:      'zipcelx sheet data is not of type array',
      invalid_type_sheet_data: 'zipclex sheet data childs is not of type array'
    };
  }

  /**
   * Holds all static XLSX template strings
   * @returns {{workbookXML: String, workbookXMLRels: String, rels: String, contentTypes: String, sheet: String}}
   */
  static get templates () {
    return {
      workbookXML:     `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"><workbookPr/><sheets><sheet name="Sheet" sheetId="1" r:id="rId1"/></sheets></workbook>`,
      WorkbookXMLRels: `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet" Target="worksheets/sheet1.xml"/><Relationship Id="rId2" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/styles" Target="styles.xml"/></Relationships>`,
      styles:          `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<styleSheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:vt="http://schemas.openxmlformats.org/officeDocument/2006/docPropsVTypes"><numFmts count="2"><numFmt numFmtId="56" formatCode="&quot;上午/下午 &quot;hh&quot;時&quot;mm&quot;分&quot;ss&quot;秒 &quot;"/><numFmt numFmtId="60" formatCode="&quot;This is &quot;\\ 0.0"/></numFmts><fonts count="1"><font><sz val="12"/><color theme="1"/><name val="Calibri"/><family val="2"/><scheme val="minor"/></font></fonts><fills count="2"><fill><patternFill patternType="none"/></fill><fill><patternFill patternType="gray125"/></fill></fills><borders count="1"><border><left/><right/><top/><bottom/><diagonal/></border></borders><cellStyleXfs count="1"><xf numFmtId="0" fontId="0" fillId="0" borderId="0"/></cellStyleXfs><cellXfs count="4"><xf numFmtId="0" fontId="0" fillId="0" borderId="0" xfId="0" applyNumberFormat="1"/><xf numFmtId="9" fontId="0" fillId="0" borderId="0" xfId="0" applyNumberFormat="1"/><xf numFmtId="60" fontId="0" fillId="0" borderId="0" xfId="0" applyNumberFormat="1"/><xf numFmtId="14" fontId="0" fillId="0" borderId="0" xfId="0" applyNumberFormat="1"/></cellXfs><cellStyles count="1"><cellStyle name="Normal" xfId="0" builtinId="0"/></cellStyles><dxfs count="0"/><tableStyles count="0" defaultTableStyle="TableStyleMedium9" defaultPivotStyle="PivotStyleMedium4"/></styleSheet>`,
      rels:            `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="xl/workbook.xml"/></Relationships>`,
      contentTypes:    `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">
<Default ContentType="application/xml" Extension="xml"/>
<Default ContentType="application/vnd.openxmlformats-package.relationships+xml" Extension="rels"/>
<Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml" PartName="/xl/worksheets/sheet1.xml"/>
<Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml" PartName="/xl/workbook.xml"/>
</Types>`,
      sheet:           `<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<worksheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"><sheetData>{placeholder}</sheetData></worksheet>`
    };
  }

  /**
   * Creates a new spreadsheet object and analyzes the data
   *
   * @param {Array} data
   */
  constructor ( data ) {
    this.raw  = data;
    this.data = this.constructor._convert( data );

    this.analyze();
  }

  /**
   * Analyzes the sheet data
   *
   * @throws {Error}
   */
  analyze () {
    if ( !Array.isArray( this.data ) ) {
      throw new Error( this.constructor.errors.invalid_type_sheet );
    }

    if ( !this.constructor._validateChildren( this.data ) ) {
      throw new Error( this.constructor.errors.invalid_type_sheet_data );
    }

    this.constructor._validateChildren( this.data );
  }

  /**
   * Builds the sheet markup
   */
  build () {
    const XMLRows = this.constructor._generateRows( this.data );
    this.sheet    = this.constructor.templates.sheet.replace( '{placeholder}', XMLRows );
  }

  /**
   * Zips the sheet and downloads it
   *
   * @param   {String}     [filename]
   * @returns {Promise<*>}
   */
  async download ( filename = this.constructor._generateRandomName() ) {
    if ( !this.sheet ) {
      this.build();
    }

    const zip = new JSZip();
    const xl  = zip.folder( 'xl' );

    xl.file( 'workbook.xml', this.constructor.templates.workbookXML );
    xl.file( 'styles.xml', this.constructor.templates.styles );
    xl.file( '_rels/workbook.xml.rels', this.constructor.templates.workbookXMLRels );
    zip.file( '_rels/.rels', this.constructor.templates.rels );
    zip.file( '[Content_Types].xml', this.constructor.templates.contentTypes );
    xl.file( 'worksheets/sheet1.xml', this.sheet );

    return FileSaver.saveAs(
      await zip.generateAsync( { type: 'blob' } ),
      `${filename}.xlsx`
    );
  }

  /**
   * Generates a random string for use as a download name.
   *
   * @param   {Number} [length] desired name length. defaults to 12.
   * @returns {string}
   * @private
   */
  static _generateRandomName ( length = 12 ) {
    return Array( length + 1 )
      .join( ( Math.random().toString( 36 ) + '00000000000000000' ).slice( 2, 18 ) )
      .slice( 0, length );
  }

  static _validateChildren ( parent ) {
    return parent.every( child => Array.isArray( child ) );
  }

  static _generateColumnLetter ( colIndex ) {
    if ( typeof colIndex !== 'number' ) {
      return '';
    }

    const prefix = Math.floor( colIndex / 26 );
    const letter = String.fromCharCode( 97 + ( colIndex % 26 ) ).toUpperCase();

    if ( prefix === 0 ) {
      return letter;
    }

    return this._generateColumnLetter( prefix - 1 ) + letter;
  }

  static _generateCellNumber ( index, rowNumber ) {
    return `${this._generateColumnLetter( index )}${rowNumber}`;
  }

  static _generateStringCell ( index, value, rowIndex ) {
    return `<c r="${this._generateCellNumber(
      index,
      rowIndex
    )}" t="inlineStr"><is><t>${this._escape( value )}</t></is></c>`;
  }

  static _generateBooleanCell ( index, value, rowIndex ) {
    return `<c r="${this._generateCellNumber(
      index,
      rowIndex
    )}" t="b"><f>${value.toString().toUpperCase()}</f><v>${Number( value )}</v></c>`;
  }

  static _generateNumberCell ( index, value, rowIndex ) {
    return `<c r="${this._generateCellNumber( index, rowIndex )}"><v>${value}</v></c>`;
  }

  static _generateDateCell ( index, value, rowIndex ) {
    const basedate = new Date( 1899, 11, 31, 0, 0, 0 );
    const dnthresh = basedate.getTime();
    const base1904 = new Date( 1900, 2, 1, 0, 0, 0 );

    const formatDate = date => {
      let epoch = date.getTime();

      if ( date >= base1904 ) {
        epoch += 24 * 60 * 60 * 1000;
      }

      return ( epoch - ( dnthresh + ( date.getTimezoneOffset() - basedate.getTimezoneOffset() ) * 60000 ) ) / ( 24 * 60 * 60 * 1000 );
    };

    // TODO: To format the cell as a date, we'd need to specify s="3" here, but that causes
    // Excel to warn about the file being broken.
    return `<c r="${this._generateCellNumber(
      index,
      rowIndex
    )}"><v>${formatDate( value )}</v></c>`;
  }

  static _formatCell ( cell, index, rowIndex ) {
    switch ( cell.type ) {
      case Number:
        return this._generateNumberCell( index, Number( cell.value ), rowIndex );

      case Boolean:
        return this._generateBooleanCell( index, Boolean( cell.value ), rowIndex );

      case Date:
        return this._generateDateCell( index, new Date( cell.value ), rowIndex );

      default:
        return this._generateStringCell( index, String( cell.value ), rowIndex );
    }
  }

  static _formatRow ( row, index ) {
    // To ensure the row number starts as in excel.
    const rowIndex = index + 1;
    const rowCells = row
      .map( ( cell, cellIndex ) => this._formatCell( cell, cellIndex, rowIndex ) )
      .join( '' );

    return `<row r="${rowIndex}">${rowCells}</row>`;
  }

  static _generateRows ( rows ) {
    return rows
      .map( ( row, index ) => this._formatRow( row, index ) )
      .join( '' );
  }

  /**
   * Escapes a string. Stolen from lodash
   *
   * @param   {string} data
   * @returns {string}
   * @private
   * @see https://github.com/lodash/lodash/blob/master/escape.js
   */
  static _escape ( data ) {
    return ( data && RegExp( this.escapeRegex.source ).test( data ) )
           ? data.replace( this.escapeRegex, ( char ) => this.escapeReplacements[ char ] )
           : data;

  }

  /**
   * Converts an array of objects into a tabular array representation. This methods assumes
   * all objects have the same keys.
   *
   * @param   {Object} data
   * @private
   */
  static _convert ( data ) {
    const keyMapper = item => Object
      .keys( item )
      .map( key => ( { value: key, type: this._matchType( key ) } ) );

    const valueMapper = item => Object
      .values( item )
      .map( value => ( { value, type: this._matchType( value ) } ) );

    if ( !Array.isArray( data ) ) {

      return [
        keyMapper( data ),
        valueMapper( data )
      ];
    }

    const first  = data[ 0 ];
    const keys   = keyMapper( first );
    const values = data.map( item => valueMapper( item ) );

    return [ keys, ...values ];
  }

  /**
   * Matches the type of a value to all supported types
   *
   * @param   {String|Number|Boolean|Date}                                  data
   * @returns {StringConstructor|NumberConstructor|BooleanConstructor|Date}
   * @private
   */
  static _matchType ( data ) {
    if ( data === true || data === false ) {
      return Boolean;
    }

    if ( data instanceof Date ) {
      return Date;
    }

    if ( !isNaN( data ) ) {
      return Number;
    }

    return String;
  }
}

export default Spreadsheet;

you have some typos in your error messages: zipclex vs zipcelx