Question

I saw somewhere someone talking about FileReader in JavaScript. What is it? What could be its use cases? Isn’t it posing security problems, as it gives JavaScript access to disk?

  var temp = new FileReader();
  temp.onload = function(e){
      // Where did it load anything? 
  };

Answer 1

This is an HTML5 feature. Check out the documentation here:

HTML5 FileReader

It’s important to note that not all (IE) browser support this functionality.