Question

从For循环中获取promise的结果的最佳方法是什么？在此示例中，代码在循环结束时resultArray未完成。

  var resultArr = [];
  var itemArray1 = [1, 2, 3, 4, 5];
  var itemArray2 = ['a','b','c','d','e'];
  for (var a = 0; a < itemArray1.length; a++) {
      for (var b = 0; b < itemArray2.length; b++) {
          myPromise(a,b)
          .then(function(result) {
                if (result != null) {
                    resultArr.push(result);
                }
          });

      }
  }  

  // resultArray is still not complete


 function myPromise(a,b) {
     return new Promise(function(resolve, reject) {
         // request to mongodb
         myTable.findOne({ _id:a, name:b }, function(err,result) {
             if (err) throw err;
             resolve(result);
         });
     });
 }

Answer 1

您可以使用def check_if_works(): import operator dict_info = {} dict_info['math 12345'] = 10 dict_info['math 1234'] = 2 dict_info['math 123'] = 1 dict_info['SCI 124'] = 16 dict_info['SCI 345'] = 2 result={} keys = {} for key, value in dict_info.iteritems(): try: if result[key.split()[0]] < value: result[key.split()[0]] = value keys[key.split()[0]] = key except KeyError: result[key.split()[0]] = value keys[key.split()[0]] = key #replace the key prefixes with full length key for key in keys.keys(): result[keys[key]] = result.pop(key) return result dict_info = check_if_works() print dict_info和forEach

的组合

Promise.all

Answer 2

在我看来，做到这一点的最简洁方法是将Promise.all()与Array#map一起使用。另外，请确保让您的功能保持干净简洁，并为其提供有意义的名称！

var itemArray1 = [1, 2, 3, 4, 5];
var itemArray2 = ['a','b','c','d','e'];

function flatten(arrays) {
    return [].concat(arrays);
}

function queryAs() {
    return Promise.all(itemArray1.map(queryBs))
        // the result is an array of arrays, so we'll flatten them here
        .then(flatten);
}

function queryBs(a) {
    return Promise.all(itemArray2.map(function (b) {
        return performQuery(a, b);
    }));
}

// resultArray is still not complete
function performQuery(a, b) {
    return new Promise(function(resolve, reject) {
        // request to mongodb
        myTable.findOne({ _id:a, name:b }, function(err,result) {
            if (err) throw err;
            resolve(result);
        });
    });
}

queryAs().then(function (results) {
    console.log(results);
});

循环使用嵌套的承诺

2 个答案: