How to pass variable to a nested callback function

Question

I'm using request npm to get http pages. I have something like that

function callbackFunction1() {
  var p = 'foo';

  request(url, callbackFunction2);
}

function callbackFunction2(err, response, body){

}

How could I pass the variable p as parameter of the callbackFunction2?

You can put the p variable outside the first callbackFunction1, then use it, as a normal variable, inside callbackFunction2. — Adam M., Aug 30 '14 at 10:19
This will solve your problem: http://stackoverflow.com/questions/13851088/how-to-bind-function-arguments-without-binding-this — eguneys, Aug 30 '14 at 10:24
What is `p` in this situation? Are you looking to simply completely replace the `body` parameter or are you looking to pass it in as an extra parameter? — James, Aug 30 '14 at 10:31

score 5 · Answer 1 · edited Aug 30 '14 at 11:46

5

I think you need to give all 3 parameters.

You can pass an anonymous function as second parameter like bellow

request(url, function(err, response, body){
    callbackFunction2(err,response, body, p);
});

edited Aug 30 '14 at 11:46

Matthias Posch

answered Aug 30 '14 at 10:19

Mritunjay

1

think you need to also take err and response as parameters in the anonymous callback function – Matthias Posch Aug 30 '14 at 10:21
1

the parameters of callbackFunction2 are three then I should pass four parameters – Mazzy Aug 30 '14 at 10:23
@Mazzy I got confused a bit, why should you pass 4 parameters, when the function expects just 3 parameters, how will you use that? – Mritunjay Aug 30 '14 at 10:26
the request callback function takes three parameters https://www.npmjs.org/package/request – Mazzy Aug 30 '14 at 10:28
@MatthiasPosch is correct that all three parameters followed by the fourth local parameter need to be passed to your original callback. It doesn't really make sense *not* to define your callback inline unless it's being reused by other callbacks to `request`. Here's a jsfiddle demonstrating: http://jsfiddle.net/jimschubert/56p9nxv5/, open the console to see the outputs. – Joseph Yaduvanshi Aug 30 '14 at 14:41

score 0 · Accepted Answer · edited May 23 '17 at 11:46

0

@facebook 's comment is they way to go.

request(url, callbackFunction2.bind(p));
...
console.log(this); // p

Read @facebook 's link to see how to do it without messing this if it matters in your use case.

edited May 23 '17 at 11:46

Community

answered Aug 30 '14 at 14:26

rollingBalls

2 Answers2