CODEWITHSUNDEEP
javascripthtmlcanvas
user1452370
user1452370

Reputation: 103

accessing object variables in javascript

So, I just started javascript and everything was working fine till i came to objects. This peace of code is supposed to create a bouncing ball in a html canvas with javascript but it doesn't work. 

  var canvas = document.getElementById("myCanvas");
  var ctx = canvas.getContext("2d");

//clear

function clear() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
}

here is my ball object

//ball

var ball = {

x: canvas.width / 2,
getX: function() {
    return this.x;
},
setX: function(a) {
    this.x = a;
},

y: canvas.height / 2,
getY: function() {
    return this.y;
},
setY: function(a) {
    this.y = a;
},

mx: 2,
getMx: function() {
    return this.mx;
},
setMx: function(a) {
    this.my = a;
},
my: 4,

getMy: function() {
    return this.my;
},

setMy: function(a) {
    this.my = a;
},
r: 10,
getR: function() {
    return this.r;
}

};

code to draw my ball 

function drawBall()
{
    ctx.beginPath();
    ctx.arc(ball.getX, ball.getY, ball.getR, 0, Math.PI * 2, true);
    ctx.fillStyle = "#83F52C";
    ctx.fill();

}

function circle(x, y, r) {
    ctx.beginPath();
    ctx.arc(x, y, r, 0, Math.PI * 2, true);
    ctx.fillStyle = "#83F52C";
    ctx.fill();
}
//draws ball and updates x,y cords 
function draw() {
    clear();
    drawBall();
    if (ball.getX() + ball.getMx() >= canvas.width || ball.getX()+ ball.getMx() <= 0) {
        ball.setMx(-ball.getMx());
    }
    if (ball.getY() + ball.getMy() >= canvas.height|| ball.getY()+ ball.getMy() <= 0) {
        ball.setMy(-ball.getMy());
    }

    ball.setX(ball.getX() + ball.getMx());
    ball.setY(ball.getY() + ball.getMy());

}

set interval 

function init() {
    return setInterval(draw, 10);
}

init();

Upvotes: 0

Views: 288

Answers (1)

user1106925
user1106925

Reputation:

Use this to reference the properties of the object on which the method is invoked.

var ball = {

    x: canvas.width / 2,
    getX: function() {
        return this.x;
    },
    setX: function(a) {
        this.x = a;
    },

    y: canvas.height / 2,
    getY: function() {
        return this.y;
    },
    setY: function(a) {
        this.y = a;
    },

    mx: 2,
    getMx: function() {
        return this.mx;
    },
    my: 4,
    getMy: function() {
        return this.my;
    },
    r: 10,
    getR: function() {
        return this.r;
    }
};

Also, to call methods, you need to use ().

ctx.arc(ball.getX(), ball.getY(), ball.getR(), 0, Math.PI * 2, true);

Otherwise you're passing the method instead of the result of calling the method.

Upvotes: 2

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