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html - Reading multiple files with Javascript FileReader API one at a time

I'm using the FileReader API to read multiple files.

<html> <body>
    <input type="file" id="filesx" name="filesx[]"
      onchange="readmultifiles(this.files)" multiple=""/>
    <div id="bag"><ul/></div>
<script>
window.onload = function() {
    if (typeof window.FileReader !== 'function') {
        alert("The file API isn't supported on this browser yet.");
    }
}

function readmultifiles(files) {
    var ul = document.querySelector("#bag>ul");
    while (ul.hasChildNodes()) {
        ul.removeChild(ul.firstChild);
    }

    function setup_reader(file) {
        var name = file.name;
        var reader = new FileReader();
        reader.onload = function(e) {
            var bin = e.target.result; //get file content

            // do sth with text

            var li = document.createElement("li");
            li.innerHTML = name;
            ul.appendChild(li);
        }
        reader.readAsBinaryString(file);
    }

    for (var i = 0; i < files.length; i++) { setup_reader(files[i]); }
}
</script> </body> </html>

The problem is that all files are read at the same time, and when the files have a total size (sum) that is very large, the browser crashes.

I want to read one file after another, so that the memory consumption is reduced.

Is this possible?

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1 Answer

0 votes
by (71.8m points)

I came up with a solution myself which works.

function readmultifiles(files) {
  var reader = new FileReader();  
  function readFile(index) {
    if( index >= files.length ) return;
    var file = files[index];
    reader.onload = function(e) {  
      // get file content  
      var bin = e.target.result;
      // do sth with bin
      readFile(index+1)
    }
    reader.readAsBinaryString(file);
  }
  readFile(0);
}

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