Chrome: Create file input from blob with Javascript?

Asked 31/7, 2012 at 12:21 Answered 26/12, 2021 at 11:10

file google-chrome input google-chrome-extension blob

Well, the files attribute of an input[type=file] is read-only. Therefore I can not write my blob data into this input element.

But if I create a new input file element using Javscript, then possible to insert blob data on creation? I am only interested in solutions working in chrome (extension) - other browsers do not matter.

Thinner answered 31/7, 2012 at 12:21 Comment(2)

I've recently tried it, and it's not possible. The only use case for wanting to modify the file in <input type=file> is when you want to change a file prior uploading. If you're looking for a method to accomplish that, use the FormData function from the XMLHttpRequest level 2 specification. Code examples can be found at stackoverflow.com/a/11628694 (possibly duplicate question?) and stackoverflow.com/a/11382138 – Hatty 31/7, 2012 at 12:31

@RobW Setting the value of a file input it also a convenient way to indicate to the user that their upload is valid/invalid, especially when they have the option to choose a file from disk or create the file in-browser (i.e. via getUserMedia). That's my use case - filling out a file input box from a microphone when the browser doesn't support that by default (which few browsers do). – Leporide 12/3, 2015 at 21:32

new File() constructor is available at chromium / chrome 38+. See File Constructor Sample , File API.

var date = new Date(),
  filename = "file-" + date.getTime() + ".html";

var generatedFile = new File(
  ["<!DOCTYPE html><html><body>" + filename + "</body></html>"]
  , filename
  , {
  type: "text/html",
  lastModified: date
  }
);

var objUrl = URL.createObjectURL(generatedFile);

console.log(generatedFile, objUrl);

var reader = new FileReader();

reader.addEventListener("load", function(event) {
  console.log(event.target.result)
});

reader.readAsText(generatedFile);

Numerable answered 4/3, 2016 at 17:41 Comment(0)

You can check my example for process file to input, url to input as blob, input to img tag preview https://vulieumang.github.io/vuhocjs/file2input-input2file/

var btnLoadUrl = document.querySelector('#loadUrl');
btnLoadUrl.addEventListener("click", ()=>{
  var url = document.querySelector('#url').value;
  loadURLToInputField(url)
});

var btnLoadImage = document.querySelector('#loadImage');
btnLoadImage.addEventListener("click", ()=>{
  var img_preview = document.querySelector('#img-preview');
  console.log(img_preview)
  loadInputFieldToPreview(img_preview)
});

var file_browser = document.querySelector('#file_browser');
var img_preview2 = document.querySelector('#img-preview2');
file_browser.addEventListener('change',()=>{
  var reader = new FileReader();
  reader.onload = function(e) {
    img_preview2.src = e.target.result
  }
  reader.readAsDataURL(document.querySelector('#file_browser').files[0]);
})

function loadURLToInputField(url){
  getImgURL(url, (imgBlob)=>{
    // Load img blob to input
    // WIP: UTF character error
    let fileName = 'hasFilename.jpg'
    let file = new File([imgBlob], fileName,{type:"image/jpeg", lastModified:new Date().getTime()}, 'utf-8');
    let container = new DataTransfer(); 
    container.items.add(file);
    document.querySelector('#file_input').files = container.files;
    // document.querySelector('#status').files = container.files;
    
  })
}

function loadInputFieldToPreview(imgElement){
  // Load preview to img tag
  var reader = new FileReader();
  reader.onload = function(e) {
    imgElement.src = e.target.result
  }
  reader.readAsDataURL(document.querySelector('#file_input').files[0]); // convert to base64 string
}

// xml json res
function httpGetAsync(url, callback){
  var req = new XMLHttpRequest();
  req.responseType = 'json';
  req.open('GET', url);
  req.onload  = function() {
    var jsonResponse = req.response;
    callback(jsonResponse)
    // do something with jsonResponse
  };
  req.send(null);
}

// xml blob res
function getImgURL(url, callback){
  var xhr = new XMLHttpRequest();
  xhr.onload = function() {
      callback(xhr.response);
  };
  xhr.open('GET', url);
  xhr.responseType = 'blob';
  xhr.send();
}

//check input status
setInterval(() => {
  var input = document.querySelector('#file_input');
  var status = document.querySelector('#status');
  if(input.value){
    status.innerHTML = 'has input'
    
  } else {
    status.innerHTML = 'empty input'
  }
}, 500);

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>URL, file to input and preview</title>
  
</head>
<body>
  <h1>Load URL to input</h1>
  <input width="100%" id='url' type="text" placeholder="paste url image here" value="https://cloudinary-res.cloudinary.com/image/upload/dpr_2.0,c_scale,f_auto,q_auto,w_156/cloudinary_logo_for_white_bg.svg">
  <button id="loadUrl">Load URL to input type file</button>
  <input id='file_input' type="file">
  <span>status input file type: <span id="status"></span></span>
 
  <h1>Load input to preview</h1>
  <button id="loadImage" >Load input above to preview</button>
  <img src="" id='img-preview' alt="img-preview">

  <h1>Load input file browser to preview</h1>
  <input type="file" name="" id="file_browser">
  <img src="" id='img-preview2' alt="preview2">

  <script src="script.js"></script>
</body>
</html>

Whither answered 26/12, 2021 at 11:10 Comment(0)

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