javascript 在嵌套函数中将项目添加到全局数组，更改不会反射(reflect)在使用 gmail api 的外部

Question

所以我有这个代码

  function addEmail(e){
      emails.push(e);
  }
  var emails = new Array;

  function getMessage( messages, callback ) {

      var get = function(len){


        //console.log(messages[len].id);
        var request = gapi.client.gmail.users.messages.get({
            'userId': 'me',
            'id': messages[len].id
          });
        request.execute(function(response){
            var e = parseMessages(response)
            //console.log(JSON.stringify(e));
            addEmail(e);    

        });
        len++;

        if(len<messages.length){
            console.log(emails.length);
            get(len);
        }
        else{
            console.log(emails.length);
            process(emails);
        }

      }
      get(0);


  };

当我尝试在方法 getMessage 之外访问电子邮件数组时，它是空的。这行代码“console.log(emails.length);”总是打印 0，
但是，当我将这行代码放入 get 方法中时，它显示值正在添加到数组中

Answer 1

when i am trying to access the emails array outside the method getMessage it is empty. this line of code "console.log(emails.length);" always prints 0

时机!

我很确定，您想构建这个:

function getMessage( messages, callback ) {
    var emails = [];
    get(0);

    function get(index){
        if(index === messages.length){
            return callback(emails);
        }

        //console.log(messages[index].id);
        var request = gapi.client.gmail.users.messages.get({
            'userId': 'me',
            'id': messages[index].id
        });

        request.execute(function(response){
            var e = parseMessages(response)
            //console.log(JSON.stringify(e));
            emails.push(e);
            get(index+1);
        });
    }
}


getMessage( someMessages, function(emails){
    console.log(emails);
})

或并行:

function getMessage( messages, callback ) {
    function done(){
        if(--pending) return;   //still work left
        callback(emails);
    }

    var pending = 1, 
        emails = Array(messages.length);

    messages.forEach(function(msg, i){
        ++pending;

        var request = gapi.client.gmail.users.messages.get({
            'userId': 'me',
            'id': msg.id
        });

        request.execute(function(response){
            emails[i] = parseMessages(response);
            done();
        });
    });

    done();
}

• 未经测试