promiseify/index.js

callback method to promiseify method

'use strict';

/**
 * promiseify
 * @param {function} method function
 * @param {object} ctx optional ctx for method
 */
function promiseify(method, ctx) {

  // check first
  if (typeof method !== 'function') {
    throw new TypeError(String(method) + ' is not a function');
  }

  return function() {

    // runtime args
    var args = [].slice.call(arguments);

    // runtime this
    ctx = ctx || this;

    return new Promise(function(resolve, reject) {

      args.push(function(err) {
        if (err) {
          return reject(err);
        }
        var arg = [].slice.call(arguments);
        if (arg.length === 2) {
          resolve.call(this, arg[1]);
        } else {
          resolve.call(this, arg.slice(1));
        }
      });

      try {
        method.apply(ctx, args);
      } catch (err) {
        reject(err);
      }
    });
  };
}

/**
 * promiseify all
 * @param  {object} o the target object
 * @return {object}   same to target object
 *
 * @example
 *   var fs = promiseify.all(require('fs'));
 *   fs.readFileAsync('file.txt', 'utf8')
 *     .then(function(s){ console.log(s); });
 *
 *   var Connection = require('mysql/lib/Connection');
 *   promiseify.all(Connection.prototype);
 *   // conn.connectAsync / conn.queryAsync / conn.endAsync available now
 */
promiseify.all = function(o) {
  Object.keys(o)
    .filter(function(m) {
      return typeof o[m] === 'function';
    })
    .forEach(function(m) {
      o[m + 'Async'] = promiseify(o[m]);
    });
  return o;
};

Object.defineProperty(promiseify, "__esModule", { value: true });
promiseify.default = promiseify;
module.exports = promiseify;