docs.sheetjs.com/docz/static/swift/SheetJSCore.swift

/* sheetjs (C) 2013-present  SheetJS -- https://sheetjs.com */
import JavaScriptCore;

enum SJSError: Error {
  case badJSContext;
  case badJSWorkbook;
  case badJSWorksheet;
};

class SJSWorksheet {
  var context: JSContext!;
  var wb: JSValue; var ws: JSValue;
  var idx: Int32;

  func toCSV() throws -> String {
    let XLSX: JSValue! = context.objectForKeyedSubscript("XLSX");
    let utils: JSValue! = XLSX.objectForKeyedSubscript("utils");
    let sheet_to_csv: JSValue! = utils.objectForKeyedSubscript("sheet_to_csv");
    return sheet_to_csv.call(withArguments: [ws]).toString();
  }

  init(ctx: JSContext, workbook: JSValue, worksheet: JSValue, idx: Int32) throws {
    self.context = ctx; self.wb = workbook; self.ws = worksheet; self.idx = idx;
  }
}

class SJSWorkbook {
  var context: JSContext!;
  var wb: JSValue; var SheetNames: JSValue; var Sheets: JSValue;

  func getSheetAtIndex(idx: Int32) throws -> SJSWorksheet {
    let SheetName: String = SheetNames.atIndex(Int(idx)).toString();
    let ws: JSValue! = Sheets.objectForKeyedSubscript(SheetName);
    return try SJSWorksheet(ctx: context, workbook: wb, worksheet: ws, idx: idx);
  }

  func writeBStr(bookType: String = "xlsx") throws -> String {
    let XLSX: JSValue! = context.objectForKeyedSubscript("XLSX");
    context.evaluateScript(String(format: "var writeopts = {type:'binary', bookType:'%@'}", bookType));
    let writeopts: JSValue = context.objectForKeyedSubscript("writeopts");
    let writefunc: JSValue = XLSX.objectForKeyedSubscript("write");
    return writefunc.call(withArguments: [wb, writeopts]).toString();
  }

  init(ctx: JSContext, wb: JSValue) throws {
    self.context = ctx;
    self.wb = wb;
    self.SheetNames = wb.objectForKeyedSubscript("SheetNames");
    self.Sheets = wb.objectForKeyedSubscript("Sheets");
  }
}

class SheetJSCore {
  var context: JSContext!;
  var XLSX: JSValue!;

  func init_context() throws -> JSContext {
    var context: JSContext!
    do {
      context = JSContext();
      context.exceptionHandler = { _, X in if let e = X { print(e.toString()!); }; };
      context.evaluateScript("var global = (function(){ return this; }).call(null);");
      context.evaluateScript("if(typeof wbs == 'undefined') wbs = [];");
      let src = try String(contentsOfFile: "xlsx.full.min.js");
      context.evaluateScript(src);
      if context != nil { return context!; }
    } catch { print(error.localizedDescription); }
    throw SJSError.badJSContext;
  }

  func version() throws -> String {
    if let version = XLSX.objectForKeyedSubscript("version") { return version.toString(); }
    throw SJSError.badJSContext;
  }

  func readFile(file: String) throws -> SJSWorkbook {
    let data: String! = try String(contentsOfFile: file, encoding: String.Encoding.isoLatin1);
    return try readBStr(data: data);
  }

  func readBStr(data: String) throws -> SJSWorkbook {
    context.setObject(data, forKeyedSubscript: "payload" as (NSCopying & NSObjectProtocol));
    context.evaluateScript("var wb = XLSX.read(payload, {type:'binary'});");
    let wb: JSValue! = context.objectForKeyedSubscript("wb");
    if wb == nil { throw SJSError.badJSWorkbook; }
    return try SJSWorkbook(ctx: context, wb: wb);
  }

  init() throws {
    do {
      self.context = try init_context();
      self.XLSX = self.context.objectForKeyedSubscript("XLSX");
      if self.XLSX == nil { throw SJSError.badJSContext; }
    } catch { print(error.localizedDescription); }
  }
}