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JavaScript

function convertDate(d){
 var parts = d.split(" ");
 var months = {
  Jan: "01",
  Feb: "02",
  Mar: "03",
  Apr: "04",
  May: "05",
  Jun: "06",
  Jul: "07",
  Aug: "08",
  Sep: "09",
  Oct: "10",
  Nov: "11",
  Dec: "12"
 };
 return parts[3]+"-"+months[parts[1]]+"-"+parts[2];
}

var d = "Fri Jan 31 2014 00:00:00 GMT-0800 (Pacific Standard Time)";
alert(convertDate(d));