Nodejs Basic Develop

最新推荐文章于 2022-07-13 11:05:56 发布

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本文介绍Node.js中如何获取系统信息如CPU数量、内存使用情况等，并演示了如何利用Node.js进行基本的文件操作，包括读写、追加、判断文件存在性和删除文件。

NodeJs 虽然是Javascript语言，但是能做服务器端语言所做的事情。比如创建监听服务，读取系统信息，读写文件等等。

1.读取CPU及内存信息

var numCPUs = require('os').cpus().length;
console.log('This computer has ' + numCPUs + 'CPUs');
var showMem = function() {
     var mem = process.memoryUsage();
     var format = function(bytes) {
          return (bytes/1024/1024).toFixed(2)+'MB';
     };
     console.log('Process: heapTotal '+format(mem.heapTotal) + ' heapUsed ' + format(mem.heapUsed) + ' rss ' + format(mem.rss));
     console.log('----------------------------------------');
};
showMem();

结果：

PS D:\NodeJsApp> node NodeApp4.js
This computer has 4CPUs
Process: heapTotal 9.30MB heapUsed 3.85MB rss 15.02MB
----------------------------------------

更多精彩内容：

console.log(os.tmpdir())

console.log(os.hostname())

console.log(os.type())

console.log(os.platform())

console.log(os.arch())

console.log(os.release())

console.log(os.totalmem())

console.log(os.freemem())
//Returns an array of objects containing information about each CPU/core installed
console.log(os.cpus())
//Get a list of network interfaces: 
console.log(os.networkInterfaces())

结果：

[ { model: 'Intel(R) Core(TM) i5-4210M CPU @ 2.60GHz',
    speed: 2594,
    times: { user: 263421, nice: 0, sys: 478671, idle: 3216515, irq: 5312 } },
  { model: 'Intel(R) Core(TM) i5-4210M CPU @ 2.60GHz',
    speed: 2594,
    times: { user: 258015, nice: 0, sys: 470390, idle: 3230062, irq: 28515 } },
  { model: 'Intel(R) Core(TM) i5-4210M CPU @ 2.60GHz',
    speed: 2594,
    times: { user: 278312, nice: 0, sys: 515921, idle: 3164234, irq: 4625 } },
  { model: 'Intel(R) Core(TM) i5-4210M CPU @ 2.60GHz',
    speed: 2594,
    times: { user: 293062, nice: 0, sys: 470578, idle: 3194828, irq: 4500 } } ]
{ 'Wi-Fi':
   [ { address: 'fe80::605c:aa7d:b906:154',
       netmask: 'ffff:ffff:ffff:ffff::',
       family: 'IPv6',
       mac: '80:00:0b:73:9a:9c',
       scopeid: 4,
       internal: false },
     { address: '192.168.1.7',
       netmask: '255.255.255.0',
       family: 'IPv4',
       mac: '80:00:0b:73:9a:9c',
...

2.事件处理(Event)

var http = require('http');

var server = http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Hello World\n');
}).listen(8124);

server.on('connection', function (stream) {
  console.log('someone connected!');
});

console.log('Server running at http://127.0.0.1:8124/');

说明：

server变量保存创建的监听对象，然后为server添加一个事件-connection，当连接成功后输出信息。

结果：

1）连接前

PS D:\NodeJsApp> node NodeApp1.js
Server running at http://127.0.0.1:8124/

2）连接后：

PS D:\NodeJsApp> node NodeApp1.js
Server running at http://127.0.0.1:8124/
someone connected!

另外，还可以添加一次性事件：

server.once('connection', function (stream) {
  console.log('Ah, we have our first user!');
});

事件监听既然可以添加，肯定也可以移除（注意这里回调函数的定义方式）：

var callback = function(stream) {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

查看监听某事件的所有listener:

server.on('connection', function (stream) {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection'))); // [ [Function] ]

3.读写文件

1）创建与读取JSON

var fs = require('fs');
fs.writeFileSync('./output.json',JSON.stringify({a:1,b:2}));
var JsonObj=JSON.parse(fs.readFileSync('./output.json'));
console.log(JsonObj);

2）写入字符串到文本文件

var fs = require('fs');
fs.writeFile('message.txt', 'Hello Node', function (err) {
  if (err) throw err;
  console.log('It\'s saved!');
});

3）追加内容到文件

var fs = require('fs');
fs.appendFile('message.txt', 'data to append', function (err) {
  if (err) throw err;
  console.log('The "data to append" was appended to file!');
});

4）判断文件是否存在

var fs = require('fs');
fs.exists('./1.txt', function (exists) {
  console.log(exists ? "it's there" : "no passwd!");
});

5）删除文件

var fs = require('fs');
fs.unlinkSync('./2.txt');
console.log('successfully deleted 2.txt');

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