How to use Javascript to read local text file and read line by line?

Issue

I have a web page made by html+javascript which is demo, I want to know how to read a local csv file and read line by line so that I can extract data from the csv file.

Solution

Without jQuery:

const $output = document.getElementById('output')
document.getElementById('file').onchange = function() {
  var file = this.files[0];

  var reader = new FileReader();
  reader.onload = function(progressEvent) {
    // Entire file
    const text = this.result;
    $output.innerText = text

    // By lines
    var lines = text.split('\n');
    for (var line = 0; line < lines.length; line++) {
      console.log(lines[line]);
    }
  };
  reader.readAsText(file);
};

<input type="file" name="file" id="file">
<div id='output'>
  ...
</div>

Remember to put your javascript code after the file field is rendered.

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