lift-p - Lift functions expecting callbacks into functions returning promises

lift-p takes functions of the form function (a1, a2, ..., an, cb) and turns them into functions of the form function (a1, a2, ..., an) -> Promise.

e.g.

  var liftP = require('lift-p');
  var assert = require('assert');

  liftP(function(a, cb){
    setTimeout(function(){
      cb(null, a);
    }, 20);
  })('foo')
  .then(function(v){
    assert(v === 'foo');
  });

If something goes wrong, the promise fails.

  liftP(function(cb){
    setTimeout(function(){
      cb('failure');
    }, 20);
  })()
  .catch(function(e){
    assert(e === 'failure');
  });

You may also pass in a value for this that will be bound after all parameters are given.

  var liftP = require('lift-p');
  var assert = require('assert');

  var C = function(v){
    this.v = v;
  };
  C.prototype.run = function(a1, cb) {
    var that = this;
    setTimeout(function(){
      cb(null, that.v + ' ' + a1);
    }, 20);
  };

  var o = new C('foo');
  liftP(o.run, o)('bar')
  .then(function(v){
    assert(v === 'foo bar');
  });