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JavaScript Object-Oriented JavaScript (2015) Constructor Functions and Prototypes Methods with Prototypes

Daniel Salvatori
Daniel Salvatori
2,658 Points
Posted by Daniel Salvatori
Daniel Salvatori
2,658 Points

Adding a method to multiple objects within an array

Hello, I need help with a task.

Say i have an array which contains a large number of objects. How can I create function which will add a method to multiple (or even all) objects with in the array?

For example a simple print method.

Thank you

2 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

If these objects are all instances of a particular class, you can add the method to the class prototype which will give it to every item at once:

// add a "print" method to every instance of "thing":
thing.prototype.print = function (arg) {
  /* your method body code */
}

If you need more specific help, please show your code.

Daniel Salvatori
Daniel Salvatori
2,658 Points
Daniel Salvatori
Daniel Salvatori
2,658 Points

Hi Steven,

thanks for the reply.

The Array looks like this:

var movieData = [

      {
        title: "The Lord of the Rings: The Two Towers",
        releaseDate: "2002",
        genres: [
          "Adventure",
          "Drama",
          "Fantasy"
        ],
        actors: [
          { firstName: "Elijah", lastName: "Wood" },
          { firstName: "Ian", lastName: "McKellen" },
          { firstName: "Viggo", lastName: "Mortensen" }
        ],
        duration: "235M",
        criticRating: 8.7,
        description: "While Frodo and Sam, now accompanied by a new guide, continue their hopeless journey towards the land of shadow to destroy the One Ring, each member of the broken fellowship plays their part in the battle against the evil wizard Saruman and his armies of Isengard."
      },
// several more objects like this with different movies

And I want to have the method print all the details of each movie.

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

These are anonymous objects. So you could create a definition for them, and then define the data as new instances of that type, or you could create the prototype method on the generic object "Object":

/* define a new method for ALL objects */
Object.prototype.printData = function ( ) {
  document.write("Title: " + this.title + "<br>");
  document.write("Date: " + this.releaseDate + "<br>");
  document.write("Genres: " + this.genres + "<br>");
  /* other properties... */
}

/* call the new method on one of the array objects */
movieData[0].printData();

Also, instead of a method you could create an ordinary function that takes one of these objects as an argument:

function printData(movie) { /* ... */ }

printData(movieData[0]);
Daniel Salvatori
Daniel Salvatori
2,658 Points
Daniel Salvatori
Daniel Salvatori
2,658 Points

I appreciate your help Steven, thank you!

Daniel Salvatori
Daniel Salvatori
2,658 Points
Daniel Salvatori
Daniel Salvatori
2,658 Points

Great, one question remaining would be how to access the values inside the "actors" array and get them to print using this. method?

I've created a function- getActors(title) - to print these values previously but i do not know how to apply it to the context of this method.

here is the code for getActors if interested

var actorNameArray = [];
var actorFirstObj = '';

function getActors (title){
for ( var i = 0; i < movieData.length; i ++){
  if (title === movieData[i].title){
    for(var j = 0; j < movieData[i].actors.length; j++)
   actorFirstObj += movieData[i].actors[j].firstName + ' ' +movieData[i].actors[j].lastName + ', ';
  actorNameArray.push(actorFirstObj);
  for(var k = 0; k < actorNameArray.length; k++){
    console.log(actorNameArray[k]);
      }
    }
  }
}

getActors('Back to the Future');

using getActors.this(title) prints every actor from every movie for each instance.

Thanks in advance.

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

The "getActors" is already an example of the kind of function I was suggesting. If you want the output to go to the page you could substitute "document.write" for "console.log":

        document.write(actorNameArray[k]);

I tested it with the previously supplied data:

getActors("The Lord of the Rings: The Two Towers");