具有可读流
var fs = require('fs');function get_line(filename, line_no, callback) { var stream = fs.createReadStream(filename, { flags: 'r', encoding: 'utf-8', fd: null, mode: 0666, bufferSize: 64 * 1024 }); var fileData = ''; stream.on('data', function(data){ fileData += data; // The next lines should be improved var lines = fileData.split("n"); if(lines.length >= +line_no){ stream.destroy(); callback(null, lines[+line_no]); } }); stream.on('error', function(){ callback('Error', null); }); stream.on('end', function(){ callback('File end reached without finding line', null); });}get_line('./file.txt', 1, function(err, line){ console.log('The line: ' + line);})直接解决方案：
您应该使用slice方法而不是循环。
var fs = require('fs');function get_line(filename, line_no, callback) { var data = fs.readFileSync(filename, 'utf8'); var lines = data.split("n"); if(+line_no > lines.length){ throw new Error('File end reached without finding line'); } callback(null, lines[+line_no]);}get_line('./file.txt', 9, function(err, line){ console.log('The line: ' + line);})for（var l in lines）不是遍历数组的最有效方法，您应该这样做：
for(var i = 0, iMax = lines.length; i < iMax; i++){ }异步方式：
var fs = require('fs');function get_line(filename, line_no, callback) { fs.readFile(filename, function (err, data) { if (err) throw err; // Data is a buffer that we need to convert to a string // Improvement: loop over the buffer and stop when the line is reached var lines = data.toString('utf-8').split("n"); if(+line_no > lines.length){ return callback('File end reached without finding line', null); } callback(null, lines[+line_no]); });}get_line('./file.txt', 9, function(err, line){ console.log('The line: ' + line);})
