在构造函数内部绘制画布时出错

Question

我在构造函数（draw）函数内编写了一个名为Circle()的函数。但是，当我调用此函数时，它将返回错误。谁能帮我解决这个问题？

这是我的代码：

var canvas = document.getElementById('canvas'),
    c = canvas.getContext('2d')

canvas.width = innerWidth
canvas.height = innerHeight
canvas.style.background = 'black'


function Circle(x, y, dx, dy, radius) {
    this.x = x
    this.y = y 
    this.dx = dx
    this.dy = dy 
    this.radius = radius
    this.circleColor = 'red'

    this.draw = function () {
        c.beginPath()
        c.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false)
        c.fillStyle = this.circleColor
        c.fill()
        c.closePath()
    }

}


var radius = Math.floor(Math.random() * 30),
    x = Math.random() * (innerWidth - radius * 2) + radius,
    y = Math.random() * (innerHeight - radius * 2) + radius,
    dx = (Math.random() - .5 ) * 10, 
    dy = (Math.random() - .5 ) * 10

    
var circle1 = Circle(x, y, dx, dy, radius)

function animate() {
    requestAnimationFrame(animate)
    c.clearRect(0, 0, innerWidth, innerHeight)

    circle1.draw()

}

animate()

<canvas id="canvas"></canvas>