从回调函数获取参数

Question

我需要从回调函数中获取参数“i”并将其移至“obj”。我读了很多相同的主题，但我仍然不明白它是如何工作的。请有人帮忙。

function getData(index,callback) 
    {
        var openReq = indexedDB.open("catalogs");
        openReq.onsuccess = function() 
        {


            var db = openReq.result;
            var transaction = db.transaction(['plants'], "readwrite");
            var objectStore = transaction.objectStore("plants");
            var objectStoreRequest = objectStore.get(index);
            var store=null;  
              objectStoreRequest.onsuccess =function(event)
              {
              store =objectStoreRequest.result;

              //console.log(store);
              return store;
              }
              transaction.oncomplete = function(event)
              {
                db.close();
                if(callback)
                    callback(store);
              }
        }
    }

......一些代码......

    for (var i = 101; i < 272; i++){
        var obj= new Object();
        getData(''+i,function (i){document.obj=i;});
        console.log(obj);
        }

Answer 1

...您想要哪个值，来自for循环的i还是来自回调的i？他们有两个不同的价值观。

回调结果

（我认为你想要的那个）

for (var i = 101; i < 272; i++){
    var obj = {}; // same as `new Object()`
    getData( i.toString(), function (result){
        obj.yourPropertyNameHere = result;
        console.log(obj);
    });
}

迭代器索引

for (var i = 101; i < 272; i++){
    // we have to store a copy of the variable `i` in the closure
    // of a function, otherwise all of the callbacks will reference
    // the final value of `i` from the loop
    (function(i_copy){

        var obj = {}; // same as `new Object()`
        getData( i_copy.toString(), function (result){
            obj.yourPropertyNameHere = i_copy;
            console.log(obj);
        });

    })(i);
}