Uncaught TypeError: Failed to execute 'readAsDataURL' on 'FileReader': parameter 1 is not of type 'Blob'

Question

I\'ve got a problem with a javascript Filereader which returns the error Uncaught TypeError: Failed to execute \'readAsDataURL\' on \'FileReader\': parameter 1 is not of type \'

Answer 1

i was getting a similar error when i would click the input but then instead of choosing an attachment, clicking cancel. so if I just wrapped the readAsDataURL call with an if statement checking if the file existed, it fixed it. see below.

onSelectFile(event) {
    let reader = new FileReader();
    reader.onload = function(){
      let output: any = document.getElementById('blah');
      output.src = reader.result;
    }
    if(event.target.files[0]){
      reader.readAsDataURL(event.target.files[0]);
    }
}