How to make a method that can affect any value type?

Question

Warning: creating extensions to native object and/or properties is considered bad form, and is bound to cause problems. Do not use this if it is for code that you are not using solely for you, or if you don't know how to use it properly

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I know you can use Object, String, Number, Boolean, etc. to define a method, something like this:

String.prototype.myFunction = function(){return this;} //only works on strings. 

But what I need to be able to do is use that on any value, and access the value in the function.

I googled, and looked here, but couldn't find anything suitable.

2/18/15 Edit: Is there any workaround to having this be a property of any Object if I use Object.prototype?
Per Request, here is the current function that is used for isString()

function isString(ins) {     return typeof ins === "string"; } 

Following on a few answers, I have come up with some code and errors caused by it.

Object.prototype.isString = function() {     return typeof this === "string"; } "5".isString() //returns false "".isString()  //returns false var str = "string" str.isString() //returns false 

Answer 1

A “dot operator function” is called a method. The cleanest way to create a method in JavaScript that can work on any data type is to create a wrapper. For example:

var Wrapper = defclass({      constructor: function (value) {          this.value = value;      },      isString: function () {          return typeof this.value === "string";      },      describe: function () {          if (this.isString()) {              alert('"' + this.value + '" is a string.');          } else {              alert(this.value + " is not a string.");          }      }  });    var n = new Wrapper(Math.PI);  var s = new Wrapper("Hello World!");    n.describe(); // 3.141592653589793 is not a string.  s.describe(); // "Hello World!" is a string.    function defclass(prototype) {      var constructor = prototype.constructor;      constructor.prototype = prototype;      return constructor;  }

By creating your own wrapper constructor you ensure that:

1. Your code doesn't mess with other peoples' code.
2. Other people's code doesn't mess with your code.
3. You keep the global scope and native prototypes clean.

Several popular JavaScript libraries like underscore and lodash create wrapper constructors for this very purpose.