Saving a zip file to a form

[DanielFrugoni]

Trying to save a zip file to a form field (pictures,zip)
let reader = new FileReader();
reader.readAsDataURL(this.miArchiv);
reader.onload = () => { console.log('Confi 4 x:' + reader.result); }

 Save the json with a huge data in the variable.
Since is allready zipped, just want to save the file, so I can down load it later like a picture.zip

Cant find the way...Help please !!