How to capture local variable value on asynchronous callback

Question

I have this for loop:

for(var i = 0; i < characters.length; i++)
{
   var character = characters[i];
   charService.get(character.name).then(function (characterData)
   {
        //I want character to be captured here, i.e. the character in the current loop
        character.data = characterData;
   });
}

As charService.get() is asynchronous, by the time the callback is executed, character is the last element of the array (because the loop has ended), hence all the previous character are left alone with no data.

How can I guarantee that character.data inside the callback is referencing the character of the loop the asynchronous method was executed?

This has been answered [here](http://stackoverflow.com/questions/11488014/asynchronous-process-inside-a-javascript-for-loop), [here](http://stackoverflow.com/questions/4288759/asynchronous-for-cycle-in-javascript) and [here](http://stackoverflow.com/questions/21184340/async-for-loop-in-node-js). — roperzh, Nov 06 '15 at 19:37

score 1 · Answer 1 · answered Nov 06 '15 at 19:37

1

You can wrap it into function

for(var i = 0; i < characters.length; i++)
{
   (function(character){
   charService.get(character.name).then(function (characterData)
   {
        //I want character to be captured here, i.e. the character in the current loop
        character.data = characterData;
   });
   })(characters[i]);
}

answered Nov 06 '15 at 19:37

user2700517

13
2

This is a nice solution! Very creative! – Matias Cicero Nov 06 '15 at 19:39

score 0 · Accepted Answer · answered Nov 06 '15 at 19:36

Try using Function.prototype.bind() at .then() function , set to character

for(var i = 0; i < characters.length; i++)
{
   var character = characters[i];
   charService.get(character.name).then(function (characterData)
   {
        //I want character to be captured here, i.e. the character in the current loop
        this.data = characterData;
   }.bind(character));
}

How to capture local variable value on asynchronous callback

2 Answers2