Creating object with dynamic keys

In the new ES2015 standard for JavaScript (formerly called ES6), objects can be created with computed keys: Object Initializer spec.

The syntax is:

var obj = {
  [myKey]: value,
}

If applied to the OP's scenario, it would turn into:

stuff = function (thing, callback) {
  var inputs  = $('div.quantity > input').map(function(){
    return {
      [this.attr('name')]: this.attr('value'),
    };
  }) 

  callback(null, inputs);
}

Note: A transpiler is still required for browser compatiblity.

Using Babel or Google's traceur, it is possible to use this syntax today.

---

In earlier JavaScript specifications (ES5 and below), the key in an object literal is always interpreted literally, as a string.

To use a "dynamic" key, you have to use bracket notation:

var obj = {};
obj[myKey] = value;

In your case:

stuff = function (thing, callback) {
  var inputs  = $('div.quantity > input').map(function(){
    var key   = this.attr('name')
     ,  value = this.attr('value')
     ,  ret   = {};

     ret[key] = value;
     return ret;
  }) 

  callback(null, inputs);
}

You can't define an object literal with a dynamic key. Do this :

var o = {};
o[key] = value;
return o;

There's no shortcut (edit: there's one now, with ES6, see the other answer).