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javascript - 在循环中正确使用 Promise javascript

问题描述

我正在尝试编写代码，使我能够按顺序从 API 获取数据并打印出我收到的内容。我有一本字典，其中包含美国各州的字典，其值是城市字典：城市代码对

var cities_forecast_dict = {'Alabama': {'Montgomery':''}, 'Alaska': {'Juneau': ''}, 'Arizona': {'Phoenix': ''}, 'Arkansas': {'Little Rock': ''}, 
'Connecticut': {'Hartford': ''}, 'Delaware': {'Dover': ''}, 'Florida': {'Tallahassee': ''}, 'Georgia': {'Atlanta': ''}, 
'Indiana': {'Indianapolis': ''}, 'Kentucky': {'Frankfort': ''}, 'Maine': {'Augusta': ''}, 'Maryland': {'Annapolis': ''}, 'Massachusetts': {'Boston': ''}, 
'Mississippi': {'Jackson': ''}, 'New Hampshire': {'Concord': ''}, 'New Jersey': {'Trenton': ''}, 'New York': {'Albany': ''}, 'North Carolina': {'Raleigh': ''}, 
'Ohio': {'Columbus': ''}, 'Pennsylvania': {'Harrisburg': ''}, 'Rhode Island': {'Providence': ''}, 'South Carolina': {'Pierre': ''}, 'Tennessee': {'Nashville': ''}, 
'Vermont': {'Montpelier': ''}, 'Virginia': {'Richmond': ''}};

我的代码应该从 Accuweather API 获取位置数据，以便每个城市各自的州应该有一个代表其唯一 id 代码的值。问题是，每当我尝试打印出cities_forecast_dict我第一次创建它时的默认值时，我都会得到它的默认值。换句话说，每个城市的价值都只是''. 我很确定这是因为 for 循环与我的主代码不同步。其他人说，当在循环中使用 Promise 时，应该创建返回 Promise 的方法，然后迭代这些方法并将每个返回的值推送到一个数组中，在该数组上.all()可以调用该方法以确保每个 Promise 都有效，但这并不适用我。如果你不能告诉我，我是一个承诺的菜鸟。

intialize_location_id()
.then(console.log(cities_forecast_dict));

function intialize_location_id(){
    for(state of Object.keys(cities_forecast_dict)){
        for(city of Object.keys(cities_forecast_dict[state])){
            var country_id = ''
            var state_local_name = ''
            fetch('http://dataservice.accuweather.com/locations/v1/cities/US/search?apikey=8iaBpn2Bl4GZtA9cgdXZT0dtpW30DGiB&q=' + city)
            .then(response => response.json())
            .then(loc => { 
                country_id = loc[0]['Country']['ID']
                state_local_name = loc[0]['AdministrativeArea']['LocalizedName']
                if (country_id == 'US' && state_local_name == state){
                    cities_forecast_dict[state][city] = loc[0]['Key']
                }
                else{
                    console.log('error! ' + loc[0]['Country']['ID'] + ' or ' + loc[0]['AdministrativeArea']['LocalizedName']+ 'or'+ city+ ' is not in the dictionary')
                }
            })
            .then(res =>{
                //intialize_forecast_data(state, city);
            })
        }
    }
}

标签： javascriptapiloopspromise

解决方案

不需要在这里使用循环，Promise.all是你的朋友。

async function getMyResults () {
    const cities = ['Montgomery', 'Juneau'];
    const promises = cities.map(city => `http://dataservice.accuweather.com/locations/v1/cities/US/search?apikey=8iaBpn2Bl4GZtA9cgdXZT0dtpW30DGiB&q=${city}`).then(res => res.json());
    const results = await Promise.all(promises);
}

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