Promise Utils (JavaScript)

promise_utils.js

var _ = require('lodash');
var Promise = require('bluebird');

var recursive = function(obj, proc, pred) {
  pred = pred || _.partial(_.identity, true);
  (function recurse(parent, val, key) {
    _.isObject(val) ? _.map(val, _.partial(recurse, val))
      : pred(val) && (parent[key] = proc(val));
  })(null, obj);
};

var pipe = function(tasks, seed) {
  return Promise.reduce(tasks, function(arg, task) { return task(arg); }
                        , seed || null);
};

var tryPipe = function(tasks, seed) {
  return Promise.try(_.partial(pipe, tasks, seed));
};

var pwhile = function(pred, act, seed) {
  return new Promise(function(resolve, reject) {
    (function loop(item) {
      var forward = function(item) {
        return pred(item) ? act(item).then(loop) : resolve(item);
      };
      return Promise.resolve(item).then(forward);
    })(seed).catch(reject);
  });
};

// recursive example
var escapeTeXChars = function(cv) {
  var escapeChars = function(str) {
    return str.replace(/[&%#_\$\{\}]/g, function(m) {
      return '\\' + m;
    });
  };
  recursive(cv, escapeChars, _.isString);
  return cv;
};

// tryPipe example
var f1 = function(s) {
  return Promise.resolve(s + ' f1');
  return Promise.reject('error f1');
};

var f2 = function(s) {
  return Promise.resolve(s + ' f2');
  return Promise.reject('error f2');
};

var f3 = function(s) {
  return Promise.resolve(s + ' f3');
  return Promise.reject('error f3');
};

tryPipe([ f1, f2, f3, console.log ], 'start').catch(console.error);

// pwhile example
var start = function(val) { return Promise.resolve(val); };
var more = function(val) { return val < 5; };
var next = function(val) {
  console.log(val);
  return Promise.resolve(val + 1);
  return (val === 3) ? Promise.reject('oh') : Promise.resolve(val + 1);
};

pwhile(more, next, start(0)).then(console.log).catch(console.error);