Javascript inheritance - can't access methods

Question

I think I'm probably doing something silly, but I'm not sure...

I have these two classes:

function Sprite()
{
}

Sprite.prototype.test1 = function()
{
    console.log("test1");
}

function Player()
{
}

Player.prototype.test2 = function()
{
    console.log("test2");
}

Player.prototype = new Sprite();
var player = new Player();

player.test1(); // this works
player.test2(); // this doesn't work..

I'm struggling to understand why test2() doesn't work, but test1() does work. If I add properties to these classes then I can access properties from both of them, I just can't call methods from the player class. What am I doing wrong?

you over-write Player.prototype.test2 when you assign a whole object to Player.prototype. If you defined test2 after, it would create the method on the new object instead, and both would work. — dandavis
– dandavis, Commented Feb 9, 2017 at 19:55

lleaff · Accepted Answer · 2017-02-09 19:56:14Z

1

When you do this:

Player.prototype.test2 = function()
{
     console.log("test2");
}

Player.prototype = new Sprite(); // Original Player.prototype gets overwritten here

You first modify a property of Player.prototype, then you reassign Player.prototype to a new object, losing the original prototype of Player.

If you reverse the order of those 2 statements, your test will pass.

answered Feb 9, 2017 at 19:56

lleaff

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