String conversion to undefined/null/number/boolean

Question

Do you know any better and faster way to convert a string to the type it represents?

I\'ve always been using this function:

var convertType = functio         


        

Answer 1

How about:

var convertType = function (value){
  var values = {undefined: undefined, null: null, true: true, false: false}
     ,isNumber = !isNaN(+(value));
  return isNumber && +(value) || !(value in values) && value || values[value];
};
convertType('null');      //=> null
convertType('something'); //=> "something"
convertType('57.321');    //=> 57.321
convertType('undefined'); //=> undefined

This seems faster @ jsPerf

var convertType = function (value){
    var v = Number (value);
    return !isNaN(v) ? v : 
         value === "undefined" ? undefined
       : value === "null" ? null
       : value === "true" ? true
       : value === "false" ? false
       : value
 }