如何使用异步功能解决以下问题

Question

I have a javascript array. I need to process each element of this array and then store the entire array into an object store. The kind of processing I do on the elements should be async. as shown in the following method.

var x = [ele1,ele2,ele3] ; 

x.forEach(function(ele,index){

if(ele == "some specific object"){
MyAPI.process("command",function(result){ 

x[index] = result; 
});

database.store(x); 

Answer 1

The problem when calculating asynchronously is that the elements aren't processed in order. The key would be to keep track of the number of results that have been processed then, and only then, call the store method. The most effective way is to move the call to the store method into the callback. That way you can call it directly after the check for the last element succeeds rather than having to do a busy/wait while checking the flag condition. Another possibility would be to raise an event when the last element is processed and have the store take place in the event handler (or something similar).

var x = [ele1,ele2,ele3] ; 
var expectedResults = 0;
var results = 0;

x.forEach(x,function(ele,index) {
     if (ele == "some specific object") {
         ++expectedResults;
     }
});

x.forEach(x,function(ele,index){

    if (ele == "some specific object"){
        MyAPI.process("command",function(result){ 
           x[index] = result;
           if (++results == expectedResults) {
              database.store(x);
           }
        });
    }
});