This uses the power of Underscore/Lodash to do a simple swap, assuming we have an array of objects each containing two fields, we want the other field.

converstates.js

var states = [
  {'name':'Alabama', 'abbrev':'AL'},
  {'name':'Alaska', 'abbrev':'AK'},
  {'name':'Arizona', 'abbrev':'AZ'},
  {'name':'Arkansas', 'abbrev':'AR'},
  {'name':'California', 'abbrev':'CA'},
  {'name':'Colorado', 'abbrev':'CO'},
  {'name':'Connecticut', 'abbrev':'CT'},
  {'name':'Delaware', 'abbrev':'DE'},
  {'name':'Florida', 'abbrev':'FL'},
  {'name':'Georgia', 'abbrev':'GA'},
  {'name':'Hawaii', 'abbrev':'HI'},
  {'name':'Idaho', 'abbrev':'ID'},
  {'name':'Illinois', 'abbrev':'IL'},
  {'name':'Indiana', 'abbrev':'IN'},
  {'name':'Iowa', 'abbrev':'IA'},
  {'name':'Kansas', 'abbrev':'KS'},
  {'name':'Kentucky', 'abbrev':'KY'},
  {'name':'Louisiana', 'abbrev':'LA'},
  {'name':'Maine', 'abbrev':'ME'},
  {'name':'Maryland', 'abbrev':'MD'},
  {'name':'Massachusetts', 'abbrev':'MA'},
  {'name':'Michigan', 'abbrev':'MI'},
  {'name':'Minnesota', 'abbrev':'MN'},
  {'name':'Mississippi', 'abbrev':'MS'},
  {'name':'Missouri', 'abbrev':'MO'},
  {'name':'Montana', 'abbrev':'MT'},
  {'name':'Nebraska', 'abbrev':'NE'},
  {'name':'Nevada', 'abbrev':'NV'},
  {'name':'New Hampshire', 'abbrev':'NH'},
  {'name':'New Jersey', 'abbrev':'NJ'},
  {'name':'New Mexico', 'abbrev':'NM'},
  {'name':'New York', 'abbrev':'NY'},
  {'name':'North Carolina', 'abbrev':'NC'},
  {'name':'North Dakota', 'abbrev':'ND'},
  {'name':'Ohio', 'abbrev':'OH'},
  {'name':'Oklahoma', 'abbrev':'OK'},
  {'name':'Oregon', 'abbrev':'OR'},
  {'name':'Pennsylvania', 'abbrev':'PA'},
  {'name':'Rhode Island', 'abbrev':'RI'},
  {'name':'South Carolina', 'abbrev':'SC'},
  {'name':'South Dakota', 'abbrev':'SD'},
  {'name':'Tennessee', 'abbrev':'TN'},
  {'name':'Texas', 'abbrev':'TX'},
  {'name':'Utah', 'abbrev':'UT'},
  {'name':'Vermont', 'abbrev':'VT'},
  {'name':'Virginia', 'abbrev':'VA'},
  {'name':'Washington', 'abbrev':'WA'},
  {'name':'West Virginia', 'abbrev':'WV'},
  {'name':'Wisconsin', 'abbrev':'WI'},
  {'name':'Wyoming', 'abbrev':'WY'}
];

/*
 * The easy way, this simply finds the other field in the array
 * that isn't to.
**/
function convertState(name, to) {
  var from = _.without(['name', 'abbrev'], to)[0];
  var exp = new RegExp('^' + name + '$', 'i');

  var selected = _.find(states, function(st) {
    return exp.test(st[from]);
  });

  return selected[to];
}

/*
 * The better way! Since we have a pattern of swapping one field for
 * another we can make it reusable. Whenever we have an array of objects
 * containing two fields, we can use this function to create a new function
 * which will swap them around for us.
**/
function makeSwappable(array, fields) {
  return function(name, to) {
    var from = _.without(array, to)[0];
    var exp = new RegExp('^' + name + '$', 'i');

    var selected = _.find(array, function(item) {
      return exp.test(item[from]);
    });

    return selected[to];
  };
}

var convertState = makeSwappable(states, ['name', 'abbrev']);