我的JavaScript代码在尝试使用keydown事件处理程序更改类中的变量时遇到问题

在我的更新中,posX应该在 W 键被按下,但什么也没发生。如果我去掉If语句,只要在调用update函数时对其进行更改,它就会工作。

class FPlayer {

    constructor(windowWidth, windowHeight, width, height, posX, posY) {

        this.width = width;
        this.height = height;
        this.posX = posX;
        this.posY = posY;
        this.windowWidth = windowWidth;
        this.windowHeight = windowHeight;
        this.x = 0;

        addEventListener("keydown", this.handler);
    }

    update() {

        if(this.x == 87) {

            this.posX += 2;
        }
    }
    draw() {

        c.beginPath();
        c.fillStyle = "blue";
        c.fillRect(this.posX, this.posY, this.width, this.height);
        c.closePath();
    }

    handler(event) {

        this.x = event.keyCode;
    }
}