Node comes with a readline module in it's core, allowing you to process a readable stream line by line.
var fs = require("fs"),
readline = require("readline");
var file = "something.csv";
var rl = readline.createInterface({
input: fs.createReadStream(file),
output: null,
terminal: false
})
rl.on("line", function(line) {
console.log("Got line: " + line);
});
rl.on("close", function() {
console.log("All data processed.");
});