accessing object method in javascript

You set the myObj variable in your example as a reference to the window.myObj variable, and afterwards you override this reference with a new object. The original window.myObj variable is still the variable you set (in window.myObj= {};);

Check this example:

(function () {
  if (!window.myObj) {
    window.myObj= { home: function() { console.log('original home'); } };
  }
  var myObj = window.myObj;
  myObj = {
    home: function () {
      console.log('hi from home');
    }, 
    details: function(){
      console.log('hi from details');
    }    
  }
})();
$(document).ready(function () {
  window.myObj.home();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

You can use the window.myObj = {...} or you can set the specific function to that variable (using myObj.home = function() { ... }).

You need to make myObj global

var myObj = undefined;
(function() {
  'use strict';
  if (!window.myObj) {
    window.myObj = {};
  }
  myObj = window.myObj;
  myObj = {
    home: function() {
      console.log('hi from home');
      return true
    },
    details: function() {
      console.log('hi from details');
      return true
    }
  }
})();

console.log(myObj.home())

You are missing ) paranthesis, also make the object global,

  var myObj;
  (function() {
    'use strict';

    if (!window.myObj) {
      window.myObj = {};
    }
    myObj = window.myObj;
    myObj = {
      home: function() {
        console.log('hi from home');
      },
      details: function() {
        console.log('hi from details');
      }
    }
  })();
  $(document).ready(function() {
    myObj.home();
  })

DEMO

This here seems to be your issue...

var myObj= window.myObj;

Since the above line of code has been placed inside of an anonymous function, only code within the scope of this function can access it.

One way we can fix your issue is by making myObj a public variable.

Before your anonymous function, place the following code...

var myObj = {};

Because this is outside of the anonymous function, myObj is declared in the global scope and therefore can be accessed from within your function.

Because of this adjustment, we can get rid of a big block of code...

if (!window.myObj) {
    window.myObj= {};
}    
var myObj= window.myObj;

Here is the final code that does what you are looking for...

var myObj = {}; // declare myObj in a global scope
(function () {    
    'use strict';
    myObj = { // since myObj is already declared as global, our function can access it
       home: function () {
          console.log('hi from home');
       }, 
       details: function(){
          console.log('hi from details');
       }    
    }
})();
myObj.home(); //testing out our code
myObj.details();

Here is a working example... http://labs.codecademy.com/D395#:workspace

you can access your window property using this:

(function () {    
    'use strict';    
    if (!window.myObj) {
        window.myObj = {};
    }    
    var myObj = window.myObj;
    myObj.home = function () {
          console.log('hi from home');
    }; 
    myObj.details = function(){
       console.log('hi from details');
    };
})();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
      $(function(){
        window.myObj.home();
        window.myObj.details();
      });
    </script>