AngularJS Example:

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">

CSS

.done-true {
  text-decoration: line-through;
  color: grey;
}

JavaScript

// angular.copy()

var mySource = {'name' : 'sakshi', 'age' : '24', 'obj' :{'key':'value'}}
var myDest = {}
angular.copy(mySource,myDest);
mySource.name = "Rohit";
console.log(mySource); // Object {name: "Rohit", age: "24", obj: Object}
console.log(myDest); // Object {name: "sakshi", age: "24", obj: Object}
console.log(mySource.obj === myDest.obj); // false

// angular.extend()

var mySource = {'name' : 'sakshi', 'age' : '24', 'obj' :{'key':'value'}}
var myDest = {}
angular.extend(myDest,mySource);
mySource.name = "Rohit";
console.log(mySource); // Object {name: "Rohit", age: "24", obj: Object}
console.log(myDest); // Object {name: "sakshi", age: "24", obj: Object}
console.log(mySource.obj === myDest.obj); // True