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
 }

Answer 2

This is a simple function which involves the use of a function to evaluate the strings. This way you can remove the part of cases' "switch". Be aware that this handles also assignments to global variables, so I recommend it only if you know anytime where is the source from(don't allow users to use this function!)

var convertType = function (value){
    try {
        return (new Function("return " + value + ";"))();
    } catch(e) {
        return value;
    }
};

You can see the jsfiddle here.

Answer 3

var string2literal = function (value){
  var maps = {
   "NaN": NaN,
   "null": null,
   "undefined": undefined,
   "Infinity": Infinity,
   "-Infinity": -Infinity
   }
  return ((value in maps) ? maps[value] : value);
};

There are many weird rules in dynamic data type converting, just map it.