Find string and delete line - Node.JS - node.js

Question

How to read file, search for string and delete line in node.js? I have tried
var fs = require('fs')
fs.readFile('shuffle.txt', function read(err, data) {
if (err) {
throw err;
}
lastIndex = function(){
for (var i = data_array.length - 1; i > -1; i--)
if (data_array[i].match('user1'))
return i;
}()
delete data_array[lastIndex];
});

Answer 1

Let's say we have a text file, shuffle.txt contains the following content
john
doe
user1
some keyword
last word
Now we read the shuffle.txt file and then search for 'user1' keyword. If any line contains the 'user1', then we will remove the line.
var fs = require('fs')
fs.readFile('shuffle.txt', {encoding: 'utf-8'}, function(err, data) {
if (err) throw error;
let dataArray = data.split('\n'); // convert file data in an array
const searchKeyword = 'user1'; // we are looking for a line, contains, key word 'user1' in the file
let lastIndex = -1; // let say, we have not found the keyword
for (let index=0; index<dataArray.length; index++) {
if (dataArray[index].includes(searchKeyword)) { // check if a line contains the 'user1' keyword
lastIndex = index; // found a line includes a 'user1' keyword
break;
}
}
dataArray.splice(lastIndex, 1); // remove the keyword 'user1' from the data Array
// UPDATE FILE WITH NEW DATA
// IN CASE YOU WANT TO UPDATE THE CONTENT IN YOUR FILE
// THIS WILL REMOVE THE LINE CONTAINS 'user1' IN YOUR shuffle.txt FILE
const updatedData = dataArray.join('\n');
fs.writeFile('shuffle.txt', updatedData, (err) => {
if (err) throw err;
console.log ('Successfully updated the file data');
});
});
Here, if a line contains 'user1' keyword, we are removing the entire line. The new shuffle.txt file will be no longer contains a line with 'user1' keyword. The updated shuffle.txt file looks like
john
doe
some keyword
last word
For more information check the doc.