JavaScript: How to pass current value to callback function?

Question

I'm trying to pass current value to callback function. I used this answers to work with, but it doesn't work for me.

for (var i = 0; i < 4; i++) {
  (function(_i) {
    var options = {
        //Options here
    };
    console.log(_i); // 0, 1, 2, 3

    LocalImageManager.download(options, function (results, _i) {
      console.log(_i);  //undefined, undefined, undefined, undefined

      //Do stuff with results
    });

  }
})(i);

The problem is function always works with "i" variable, which is undefined after the loop finished.

Use IIFE around the `download()`. `LocalImageManager.download(options, function (results, _i) { (function (_i) { console.log(_i); //Do stuff with results })(i); });` — Tushar, Jul 14 '16 at 11:00
do not pass it as an argument just use in console.log() and see what happens — Ruben Karapetyan, Jul 14 '16 at 11:01
`_i` will be accessible to all nested functions. You don't need to pass it as an argument. — evolutionxbox, Jul 14 '16 at 11:02
You have declared `_i` again in `function (results, _i)`, causing `_i` not getting from loop, change to `function (results)` — Jagdish Idhate, Jul 14 '16 at 11:02
@Liam - it looks like it has been closed around. It's just the OP has put the closing brackets for the IIFE in the wrong place. — evolutionxbox, Jul 14 '16 at 11:06
what does LocalImageManager.download do/accept as an argument? — Liam, Jul 14 '16 at 11:06
yes, well spotted @evolutionxbox This has multiple problems... — Liam, Jul 14 '16 at 11:07

score 0 · Accepted Answer · answered Jul 14 '16 at 11:12

for (var i = 0; i < 4; i++) {
  (function(_i) {
    var options = {
      //Options here
    };
    console.log(_i); // 0, 1, 2, 3

    LocalImageManager.download(options, function (results) {
      console.log(_i); // 0, 1, 2, 3

      //Do stuff with results
    });
  })(i);
}

score -1 · Answer 2 · edited Jul 14 '16 at 11:04

-1

You need to change the definition of LocalImageManager.download because your callback method is calling from there only. You can send the value of _i in different parameter or with options you passed in function and use at the time of calling the callback method.

edited Jul 14 '16 at 11:04

Liam

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answered Jul 14 '16 at 11:03

Anuj Kumar

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JavaScript: How to pass current value to callback function?

2 Answers2