javascriptfilefileapihtml-input

Add a File (JS object) to input type="file"


I need a way to add a File object to a file input field.

Note that I do not want to set the value of the file field. (which is a security risk, ... I know that)
I already have the file itself (and all its contents!)

I'm creating the File object like this:

canvas.toBlob(function(blob) {
  var file = new File([blob], 'file.png');
  // and now I want to add MY File to the input here
});

Please don't tell me about how to upload the File, I know about XMLHttpRequest Level 2. I want to upload the File to an external website (potentially using a userscript or something similar).

So, how can I achieve that? Or if it's not possible: why can't I add a File that I actually own (because I created it in the Browser (as a virtual File, which does not even exist in the users filesystem)) to an input field that I own too? (technically the input field could be my own, that does not matter here)


Solution

  • Yes it is possible:

    To load file from blob:

    
      let fileInputElement = document.getElementById('file_input');
      let container = new DataTransfer();
      // Here load or generate data
        let data = new Blob();
        let file = new File([data], "g"+i+".jpg",{type:"image/jpeg", lastModified:new Date().getTime()});
        container.items.add(file);
      fileInputElement.files = container.files;
    
    

    To load file from another file input:

    
      let input1 = document.getElementById('file_input');
      let input2 = document.getElementById('some_other_input')
      let container = new DataTransfer();
       [...input2.files].map(file=>container.items.add(file));
      input1.files = container.files;
    
    

    https://jsfiddle.net/Kartearis/gmhwnaz6/3/