Check hasOwnProperty in for...in

gistfile1.js

// Check hasOwnProperty in for...in

// When you are using the for...in loop in JavaScript
// you must be careful to also check the object
// you are enumerating to see if it contains
// the property before proceeding. The reason for 
// this is that the for...in loop also iterates
// over the prototype's properties as well */

var Person = function( firstName, lastName ) {
  this.firstName = firstName;
  this.lastName = lastName;
  return this;
};

Person.prototype = {
  isMarried : false,
  hasKids: false
};

var john = new Person( "John", "Smith" ),
  linda = new Person( "Linda", "Davis" );

john.isMarried = true;

console.log( "Not Checking hasOwnProperty" );
for ( name in john ) {
  console.log( name + ": " + john[name] ); 
  //Outputs
  //  firstName: John 
  //  lastName: Smith
  //  isMarried: true
  //  hasKids: false
}

console.log( "Checking hasOwnProperty" );
for ( name in linda ) {
  if ( linda.hasOwnProperty(name) ) {
    console.log( name + ": " + linda[name] ); //Outputs: firstName, lastName
    //Outputs
    //  firstName: Linda
    //  lastName: Davis
  }
}
​