What could be causing the error when trying to confirm the file type?

I am trying to detect files with types image or video. However, despite checking for the correct file type, I am still encountering errors. Below is my code:

app.component.ts

startUpload(event: FileList)
  {
    const file = event.item(0);
    if((file.type.split('/')[0] !== 'video') || (file.type.split('/')[0] !== 'image'))
    {
      alert(file.type.split('/')[0]);
      return;
    }
  }

When uploading video/image files, the alert box displays video/image accordingly. Please advise on what changes need to be made.

angulartypescriptangular9

Answer №1

It appears that your reasoning is flawed as having (x!==y) || (x!==b) will always evaluate to true.

You may want to consider using '&&' instead of '||' in your if statement for accurate logic.

Answer №2

Allow me to introduce you to De Morgan's law. Put simply, it states:

  • not (A or B) = not A and not B
  • not (A and B) = not A or not B

In your particular scenario, you must check if the file type is neither 'video' nor 'image'. You can achieve this by either:

const fileType = file.type.split('/')[0];
if((fileType !== 'video') && (fileType !== 'image')) {
  alert(fileType);
  return;
}

or

const fileType = file.type.split('/')[0];
if(!((fileType === 'video') || (fileType === 'image'))) {
  alert(fileType);
  return;
}

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