FileReader.onload is not running in android

FileReader onload is not running in android, but runs well in web.
How can I solve this problem?
help me!!!

file-service.ts

import { Injectable } from '@angular/core';
import * as XLSX from 'xlsx';

type AOA = Array<Array<any>>;

@Injectable()
export class FileService {

  constructor() {}

  async uploadExcel(file: File): Promise<AOA> {
    return new Promise<AOA>((resolve, reject) => {
      let data: AOA = [];

      console.log("uploadExcel - file: " + file.name);
      
      /* wire up file reader */
      const reader = new FileReader();
      reader.onload = (e: any) => {

        console.log("This log does not print in android.");

        ...
        ...
        resolve(data);
      };
      reader.readAsBinaryString(file);
    });
  }
}

ionic Info

cli packages:

@ionic/cli-utils  : 1.12.0
ionic (Ionic CLI) : 3.12.0

global packages:

cordova (Cordova CLI) : 7.0.1

local packages:

@ionic/app-scripts : 2.1.3
Cordova Platforms  : android 6.2.3
Ionic Framework    : ionic-angular 3.6.0

System:

Android SDK Tools : 26.0.2
Node              : v6.10.3
npm               : 5.3.0
OS                : Windows 10
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