How to open a js file locally?

Question

JavaScript

for example, there is an input with the file type and by clicking on the button you need to find out the number of characters in the file without uploading it to the server, how to implement it?

Answer 1

const file = // здесь файл с инпута; 
const reader = new FileReader()

reader.onloadend = function(e) {
    if (e.target.readyState == FileReader.DONE) { 
      console.log(e.target.result.length) 
    }
};

reader.readAsText(file)