nodejs-传递全局变量以承诺解析中的回调

Question

consider this code

for (var i = 0; i < data.length; i++){
    query.equalTo("objectId",data[i].id).first().then(
        function(object){
            object.set("username", data[i].username);
            object.save();
        }
    );
}

in this example data[i] inside the then callback is the last element of the array

consider this 2nd example that normally work in javascript world

assume we use some API which connect to mongodb and has function called update

for (var i = 0; i < data.length; i++){
    query.eq("_id",data[i].id).update(data[i].username);
}

eq returns the object, update updates that object and save it.

will it not be awesome if something like this is possible ... (not sure if it will also even work)

for (var i = 0; i < data.length; i++){
    query.equalTo("objectId",data[i].id).first().then(
        function(object, data[i]){
            object.set("username", data.username);
            object.save();
        }
    );
}

Answer 1

This actually doesn't work only because of scoping var . You can get the sample running as desired just by:

a) using let instead of var

b) creating a new scope for i (this is what let basically does). (In the anonymous fn, I used ii instead of i just for clarity. i would also work):

for (var i = 0; i < data.length; i++){
    (function(ii) {
        query.equalTo("objectId",data[ii].id).first().then(
            function(object){
                object.set("username", data[ii].username);
                object.save();
            }
        );
    })(i)
}

Answer 2

the best way to solve this problem with parse is to use recursivity

   ... 

   var do = function(entries, i){
        if (entries[i]){

            let user = data[i];

            query.equalTo("objectId", user.id).first().then(
                function(object){
                    object.set("username", user.username);
                    object.save();
                }
            ).then(
                function(){
                    return do(entries, i + 1);
                }
            );
        }
    }