function displayName() {

  console.log(this.name);

}

​

var obj1 = {name: "Deepak", displayName: displayName};

var obj2 = {name: "Chetan", displayName: displayName};

​

obj1.displayName();   

// Here value of "this" is obj1 and it display "Deepak"

​

obj2.displayName();    

// Here value of "this" is obj2 and it display "Chetan"