CODEWITHSUNDEEP
javascript
Alex Vaghin
Alex Vaghin

Reputation: 295

How to load part of the big file with JavaScript?

I have a 1GB file with text data. I need to load 100 bytes starting from N byte using browsers JavaScript into the memory. How do I do that?

Upvotes: 2

Views: 841

Answers (1)

num8er
num8er

Reputation: 19372

Use File API:

function fileReaderApiSupported() {
  return (window.File && window.FileReader && window.FileList && window.Blob);
}
    
function readNBytesOfFile(size, inputId) {
  if (!fileReaderApiSupported()) {
    alert('FileReader API unsupported');
    return;
  }
    
  var readFrom = document.getElementById(inputId);
  if (!readFrom || !readFrom.files || !readFrom.files.item(0)) {
    alert('No file');
    return;
  }
  
  var countOfBytesToRead = parseInt(size);
  var readFromFile = readFrom.files.item(0);
  
  var fileReader = new FileReader();
  var chunk = readFromFile.slice(0, countOfBytesToRead);
  
  fileReader.onload = function() {
    var result = fileReader.result;
    document.getElementById('result').innerText = result;
  };
  fileReader.readAsText(chunk);
}
<input id="my-file-input" type="file">
<button onclick="readNBytesOfFile(100, 'my-file-input')">READ</button>

<hr/>

<div id="result"></div>

also You can use LineReader to read by chunk and stop reading after 100 bytes.

Upvotes: 2

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