How to remove last line in the text(.txt) file using Javascript

Question

I have:

let removeString = (fileName, strToRemove) => {
    fs.readFile(fileName, 'utf8', function(err, data){
    let toRemove = data.replace(strToRemove+'\n','')
    fs.writeFile(fileName, toRemove)
    })
};

This successfully removes non first or last line, but how do I remove from

first
second
third

First or third using fs?

Answer 1

You can use split to split the file into an array of lines then remove whichever line you want, then rejoin the array into a string using join then write the file.

Example:

let removeString = (fileName, strToRemove) => {
    fs.readFile(fileName, 'utf8', function(err, data){
        let splitArray = data.split('\n');
        splitArray.splice(splitArray.indexOf(strToRemove), 1);
        let result = splitArray.join('\n');
        fs.writeFile(fileName, result)
    })
};

Answer 2

The above solution is not optimized for a very large file as it reads the whole file. If you are on non-windows platform, you can run unix tail command. If on windows, you can look at read-last-lines .

Look at this excellent answer