Promise: how to pass function with parameters?

Question

In the following test code, I try to pass predefined function with parameters (i.e., t2, t3) to then. But it complains "r" not defined.

var Promise = require('bluebird');

var t2 = function(r) {
    console.log("2r: " + r);
    return 2 * r;
};

var t3 = function(r) {
    console.log("3r: " + r);
    return 3 * r;
};

new Promise(function(resolve, reject) {

    setTimeout(function() {
        resolve(1);
        reject(2)
    }, 1000);
})
.then(t2(r), t3(r))
.then(t2(r), t3(r))
.then(t2(r), t3(r));

Answer 1

Just pass the function names instead:

var t2 = function(r) {
  console.log("2r: " + r);
  return 2 * r;
};

var t3 = function(r) {
  console.log("3r: " + r);
  return 3 * r;
};

new Promise(function(resolve, reject) {

    setTimeout(function() {
      resolve(1);
      reject(2)
    }, 1000); // (*)

  })
  .then(t2, t3)
  .then(t2, t3)
  .then(t2, t3);

If you actually want to pass additional parameters that you know beforehand, make t2 and t3 higher-order functions that return functions, so that you can invoke inside a .then's parameter list:

var t2 = extra => r => {
  console.log("2r: " + r);
  console.log('extra param: ' + extra);
  return 2 * r;
};

var t3 = extra => r => {
  console.log("3r: " + r);
  console.log('extra param: ' + extra);
  return 3 * r;
};


const r = 'foo';
new Promise(function(resolve, reject) {

    setTimeout(function() {
      resolve(1);
      reject(2)
    }, 1000); // (*)

  })
  .then(t2(r), t3(r))
  .then(t2(r), t3(r))
  .then(t2(r), t3(r));