等到條件成立爲止？

Question

我在JavaScript中使用navigator.geolocation.watchPosition，我想要一種方法來處理用戶可能會在watchPosition找到它的位置之前提交依賴於位置的表單的可能性。

理想情況下，用戶會定期看到「等待位置」消息，直到獲取位置，然後表單將提交。

但是，由於缺少wait函數，我不確定如何在JavaScript中實現此功能。

當前代碼：

var current_latlng = null; 
function gpsSuccess(pos){ 
    //console.log('gpsSuccess'); 
    if (pos.coords) { 
     lat = pos.coords.latitude; 
     lng = pos.coords.longitude; 
    } 
    else { 
     lat = pos.latitude; 
     lng = pos.longitude; 
    } 
    current_latlng = new google.maps.LatLng(lat, lng); 
} 
watchId = navigator.geolocation.watchPosition(gpsSuccess, 
        gpsFail, {timeout:5000, maximumAge: 300000}); 
$('#route-form').submit(function(event) { 
    // User submits form, we need their location... 
    while(current_location==null) { 
     toastMessage('Waiting for your location...'); 
     wait(500); // What should I use instead? 
    } 
    // Continue with location found... 
}); 

Answer 1

你可以使用一個超時嘗試重新提交表單：

$('#route-form').submit(function(event) { 
    // User submits form, we need their location... 
    if(current_location==null) { 
     toastMessage('Waiting for your location...'); 
     setTimeout(function(){ $('#route-form').submit(); }, 500); // Try to submit form after timeout 
     return false; 
    } else { 
     // Continue with location found... 
    } 
}); 

Answer 2

你要使用setTimeout：

function checkAndSubmit(form) { 
    var location = getLocation(); 
    if (!location) { 
     setTimeout(checkAndSubmit, 500, form); // setTimeout(func, timeMS, params...) 
    } else { 
     // Set location on form here if it isn't in getLocation() 
     form.submit(); 
    } 
} 

...其中getLocation查找您的位置。

Answer 3

就個人而言，我用一個waitfor()函數封裝了setTimeout()：

//********************************************************************** 
// function waitfor - Wait until a condition is met 
//   
// Needed parameters: 
// test: function that returns a value 
// expectedValue: the value of the test function we are waiting for 
// msec: delay between the calls to test 
// callback: function to execute when the condition is met 
// Parameters for debugging: 
// count: used to count the loops 
// source: a string to specify an ID, a message, etc 
//********************************************************************** 
function waitfor(test, expectedValue, msec, count, source, callback) { 
    // Check if condition met. If not, re-check later (msec). 
    while (test() !== expectedValue) { 
     count++; 
     setTimeout(function() { 
      waitfor(test, expectedValue, msec, count, source, callback); 
     }, msec); 
     return; 
    } 
    // Condition finally met. callback() can be executed. 
    console.log(source + ': ' + test() + ', expected: ' + expectedValue + ', ' + count + ' loops.'); 
    callback(); 
} 

我用我的waitfor()功能採用以下方式：

var _TIMEOUT = 50; // waitfor test rate [msec] 
var bBusy = true; // Busy flag (will be changed somewhere else in the code) 
... 
// Test a flag 
function _isBusy() { 
    return bBusy; 
} 
... 

// Wait until idle (busy must be false) 
waitfor(_isBusy, false, _TIMEOUT, 0, 'play->busy false', function() { 
    alert('The show can resume !'); 
}); 

Answer 4

這就是什麼承諾發明和實施（因爲OP問他的問題）。

查看所有各種實現，例如promise_s.org