() vs. ||

using-parens.js

Promise.prototype = {

  get: function(key) {
    return this.then({ (obj) obj[key]; });
  },

  put: function(key, val) {
    return this.then({ (obj) obj[key] = val });
  },

  call: function(key, ...args ) {
    // Can this Expression form have line breaks?
    return this.then({ (obj) 
      obj[key].apply(obj, args) 
    });
  },

  addCallback: function(callback) {
    return this.then(callback);
  },

  addErrback: function(errback) {
    // This was previously a no-op function expression
    return this.then({() }, errback);
  }
  ....
};

using-pipes.js

Promise.prototype = {

  get: function(key) {
    return this.then({|obj| obj[key]; });
  },

  put: function(key, val) {
    return this.then({|obj| obj[key] = val; });
  },

  call: function(key, ...args ) {
    return this.then({|obj|
      obj[key].apply(obj, args);
    });
  },

  addCallback: function(callback) {
    return this.then(callback);
  },

  addErrback: function(errback) {
    // This was previously a no-op function expression
    return this.then({||}, errback);
  }
  ....
};