Ionic 3.20.0 FileReader event not firing but Ionic 4.2.1 can

Ionic Framework ionic-v3
1

I have build my project in different computers and get different result.

The first computer: Ionic Info

Ionic:

ionic (Ionic CLI) : 4.2.1 (/usr/local/lib/node_modules/ionic)
Ionic Framework : ionic-angular 3.9.2
@ionic/app-scripts : 3.2.0

Cordova:

cordova (Cordova CLI) : 8.1.2 (cordova-lib@8.1.1)
Cordova Platforms : android 7.1.1
Cordova Plugins : no whitelisted plugins (19 plugins total)

System:

NodeJS : v8.11.3 (/usr/bin/node)
npm : 6.2.0
OS : Linux 4.15

FileReader only work when I put await in reader.readAsDataURL();

The second computer:

Ionic info

cli packages: (/usr/local/lib/node_modules)

@ionic/cli-utils  : 1.19.2
ionic (Ionic CLI) : 3.20.0

global packages:

cordova (Cordova CLI) : 8.0.0

local packages:

@ionic/app-scripts : 3.1.8
Cordova Platforms  : ios 4.5.4
Ionic Framework    : ionic-angular 3.9.2

my code:

    async downloadFromURL(fileName, mimeType, url){
        return new Promise((resolve,reject) => {
            try{
                var self = this;
                var xhr = new XMLHttpRequest();
                xhr.open('GET', url, true);
                xhr.responseType='blob';  
                xhr.onloadend = async function(e) {
                    if (xhr.status == 200)
                    {
                        var reader = new FileReader();
                        reader.onloadend = async function(event){
                            var response = self.insertFile({
                                'type': mimeType,
                                'title': fileName
                            }, event.target["result"].split(',')[1]);
                            resolve(response);
                        }
                        await reader.readAsDataURL(xhr.response);
                    }
                };
                xhr.send();
            } catch (error) {
                reject();
                console.log("error", error);
            }
        });
    }

So, my question is, how can I fix this without update ionic and cordova?

And sorry for my bad english :smiley:

Thanks in advance.