[英]How to re-structure this for loop so the next iteration doesn't happen until an asynchronous api call completes
因此,在下面,我們有一個類似於school [key] = value的數組。
for(key in schools) {
geocoder = new google.maps.Geocoder();
var address = schools[key];
var org_code = key;
geocoder.geocode({ 'address': address}, function(results, status) {
//callback function
})
}
我需要在回調函數中使用key / org_code,但是顯然for循環的迭代速度比geocode api調用完成的速度快,因此回調函數中使用了錯誤的密鑰。
我試圖使用array.shift將上面的內容重寫為一個函數,並在回調中使用該函數,但是我無法做到這一點……因為一件事,我無法使用該方法訪問鍵。
您可以使用閉包:
for(key in schools) {
(function(key) {
geocoder = new google.maps.Geocoder();
var address = schools[key];
var org_code = key;
geocoder.geocode({ 'address': address}, function(results, status) {
//callback function
})
})(key)
}
使用立即調用的函數表達式創建一個閉合,為每次迭代確定變量的范圍:
for (key in schools) {
geocoder = new google.maps.Geocoder();
var address = schools[key];
var org_code = key;
(function(address, org_code) {
geocoder.geocode({
'address': address
}, function (results, status) {
//callback function
})
})(address, org_code);
}
使用閉包的另一個建議:
for(key in schools) {
geocoder = new google.maps.Geocoder();
var address = schools[key];
var org_code = key;
geocoder.geocode({ 'address': address }, function(org_code, address) {
return function (results, status) {
// use address and org_code here
};
}(org_code, address))
}
使用遞歸函數。 獲得關鍵-重新格式化學校陣列。
var geocoder = new google.maps.Geocoder();
function geocodeNext(sch) {
var item = sch.shift();
var address = item['address'];
var key = item['key'];
geocoder.geocode({ 'address': address}, function(results, status) {
//do something with key
geocodeNext(sch);
})
}
var schools1 = [];
for var (key in schools) {
schools1.push({'address': schools[key], 'key': key});
}
geocodeNext(schools1);
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