nodejs如何按行读取文件

The eachLine function reads each line of the given file. Upon each new line, the given callback function is called with two parameters: the line read and a boolean value specifying whether the line read was the last line of the file. If the callback returns false, reading will stop and the file will be closed.

var lineReader = require('line-reader');

lineReader.eachLine('file.txt', function(line, last) {
  console.log(line);

  if (/* done */) {
    return false; // stop reading
  }
});
eachLine can also be used in an asynchronous manner by providing a third callback parameter like so:

var lineReader = require('line-reader');

lineReader.eachLine('file.txt', function(line, last, cb) {
  console.log(line);

  if (/* done */) {
    cb(false); // stop reading
  } else {
    cb();
  }
});
The eachLine function also returns an object with one property, then. If a callback is provided to then, it will be called once all lines have been read.

var lineReader = require('line-reader');

// read all lines:
lineReader.eachLine('file.txt', function(line) {
  console.log(line);
}).then(function () {
  console.log("I'm done!!");
});
For more granular control, open, hasNextLine, and nextLine maybe be used to iterate a file:

// or read line by line:
lineReader.open('file.txt', function(reader) {
  if (reader.hasNextLine()) {
    reader.nextLine(function(line) {
      console.log(line);
    });
  }
});