How to create a constructor function?

Question

Problem: I'm trying to create a constructor function named Wizard that takes 2 parameters: name and spells, and then create a Wizard object:

"Each particular instance of wizard must have a name property (a string), a spells property which is an array of strings, and a castSpell method capable of returning a random spell in string format."

The object has the following properties: name is "Gorrok" (string), and spells is "abracadabra" and "cadabraabra" (array).

Objective: to invoke the castSpell method to display a random spell like so: Gorrok : abracadabra

Code: I've only written the following code so far, and I'm stuck at this stage!

function Wizard(name, spells){
    this.name = name;
    this.spells = [spells];
    this.castSpell = function(){
        var v = Math.random();
        if (v >= 1)
            document.write(this.name + " :  " + this.spells[0]);
        else
            document.write(this.name + " :  " + this.spells[1]);
    }
}
var w = new Wizard("Gorrok", "abracadabra", "cadabraabra");
w.castSpell();

nicael · Accepted Answer · 2016-07-23 19:50:12Z

2

So, Math.random() will return a number between 0 and 1, so it'll never be bigger than 1.

Also, you can't convert the remaining arguments to an array the way you have.

Simplest fix:

function Wizard(name, spells){
    this.name = name;
    this.spells = spells; // assume spells is already an array
    this.castSpell = function(){
        var v = Math.random();
        if (v >= 0.5)
            document.write(this.name + " :  " + this.spells[0]);
        else
            document.write(this.name + " :  " + this.spells[1]);
    }
}
var w = new Wizard("Gorrok", ["abracadabra", "cadabraabra"]);
w.castSpell();

edited Jul 23, 2016 at 19:50

nicael

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answered Jul 23, 2016 at 19:49

Paul

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Comments

user6630018 · Accepted Answer · 2016-07-23 20:40:05Z

1

I think Paul's answer is correct. Also, for functions not in ctor, use prototype. Prototypes also allow you add member vars that are not defined in constructor.

Here's an example from w3:

function Person(first, last, age, eyecolor) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eyecolor;
}
Person.prototype.nationality = "English";

answered Jul 23, 2016 at 20:40

user6630018

1 Comment

Paul Over a year ago

It's worth pointing out that using the prototype has an added benefit on memory allocation in most javascript runtime environments. When a function is defined in the constructor, it allocates a new instance of the function to each instance of the object, while using the prototype as this answerer has done will allocate only one copy of the function to all instances of the class.

Freez · Accepted Answer · 2016-07-23 20:06:49Z

0

You can also use Math.round() to get 0 or 1 randomly

var v = Math.round( Math.random() );
document.write(this.name + " :  " + this.spells[v]);

answered Jul 23, 2016 at 20:06

Freez

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2 Comments

ratboy Over a year ago

This way of shuffling was new to me, I like what you did there. Exactly in which situations would you use Math.round(Math.random())? And can you use other math classes within itself?

Freez Over a year ago

Math.random returns a float between 0 and 1, Math.round rounds a float to the nearest integer. You are not limited when you use Math.{someFunction} result. It can be written like var floatBetween0and1 = Math.random(); var number0or1 = Math.round(floatBetween0and1)

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