Anil Pediredla Anil Pediredla -4 years ago 133
Node.js Question

Remove line from file without mutating the buffer variable in node js

I am new to Nodejs

I have written a function that reads contents from a file and stores into a variable as an array. And finally I am mutating the variable and writing it to a file. See below:

function(file, item) {
return fs.readLine(file).then(function(contents) {
var data = contents.split(/\n/);
data.splice(data.indexOf(item), 1);
return fs.writeFile(file, data.join(/\n/));

Is there a way to do the same without mutating the variable or even having had to store the contents of a file into a variable and delete it in node js?


Answer Source

If you don't want to mutate the variable with data.splice() then you can use data.slice() that doesn't mutate the original array. See the docs:

Also instead of reading the contents of the file into a variable, you can create a readable stream and filter out the line that you don't want.

See how I created my filt module that filters lines of standard input:

The source code and a lot of examples are on GitHub:

Basically what you can do here is - using the handy split module - something like this:

fs.createReadStream(file).pipe(split()).on('data', (line) => {
    // if line is something ... etc.
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