【Promise】Promise實現請求超時處理（基本版）

首先是沒有加入請求超時的情況：

var http = require('http');
var url = require('url');

function get(addr) {  
  return new Promise(function(resolve, reject) {
    var url_obj = url.parse(addr);
    var options = {
      hostname: url_obj.hostname,
      path: url_obj.path,
      method: 'GET'
    };

    var req = http.request(options, function(res) {
      res.setEncoding('utf8');

      var data = '';
      res.on('data', function (chunk) {
        data += chunk;
      });
      res.on('end', function () {
        data = JSON.parse(data);
        resolve(data);
      });
    });

    req.on('error', function(e) {
      reject(e)
    });
    req.end();
  });
}

get('http://demos.so/result/homework.promise.userInfo').then(function (args) {
  return Promise.all([get('http://demos.so/result/userid=' + args['_id']), get('http://demos.so/result/student=' + args['_id'])]);
}).then(function (args) {
  console.log(args);
}).catch(function(err){
  console.log(err);
});

 

再看一下加入超時的代碼：

var http = require('http');
var url = require('url');

function delayPromise(ms) {
    return new Promise(function (resolve) {
        setTimeout(resolve, ms);
    });
}
function timeoutPromise(promise, ms) {
    var timeout = delayPromise(ms).then(function () {
            throw new Error('Operation timed out after ' + ms + ' ms');
        });
    return Promise.race([promise, timeout]);
}

function get(addr) {  
  return new Promise(function(resolve, reject) {
    var url_obj = url.parse(addr);
    var options = {
      hostname: url_obj.hostname,
      path: url_obj.path,
      method: 'GET'
    };

    var req = http.request(options, function(res) {
      res.setEncoding('utf8');

      var data = '';
      res.on('data', function (chunk) {
        data += chunk;
      });
      res.on('end', function () {
        data = JSON.parse(data);
        resolve(data);
      });
    });

    req.on('error', function(e) {
      reject(e)
    });
    req.end();
  });
}


timeoutPromise(get('http://demos.so/result/homework.promise.userInfo'),1000).catch(function (err) {
  console.log(err);
}).then(function (args) {
  return Promise.all([timeoutPromise(get('http://demos.so/result/userid=' + args['_id']), 1000), timeoutPromise(get('http://demos.so/result/student=' + args['_id']), 1000)]);
}).then(function (args) {
  console.log(args);
}).catch(function (err) {
  console.log(err);
});

　　原理其實很簡單，就是利用Promise.race，我們先創建一個Promise，里面用setTimeout進行處理，然后將新創建的Promise與我們之前使用的Promise"比賽"一下。