My red square wont show up because: "speedX and speedY aren't defined"-console

So I am following this game making tutorial for javascript and I just really can't find what I did that would make it so that my red square isn't showing up on screen. I do, in fact, think it is a problem with the speed because when i changed the speed of the object in the console, it appeared... then flew off screen.

Here is my code:

    <!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
    border:1px solid #d3d3d3;
    background-color: #f1f1f1;
}
</style>
</head>
<body onload="startGame()">
<script>

var myGamePiece;

function startGame(){
    myGamePiece = new component(30, 30, "red", 10, 120);
    myGameArea.start();
}

var myGameArea = {
    canvas: document.createElement("canvas"),
    start: function(){
        this.canvas.width = 480;
        this.canvas.height = 270;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.interval = setInterval(updateGameArea, 20);
    },
    clear: function(){
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}

function component(width, height, color, x, y){
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;
    this.x = x;
    this.y = y;
    this.update = function(){
        ctx = myGameArea.context;
        ctx.fillStyle = color;
        ctx.fillRect(this.x, this.y, this.width, this.height);
    }
    this.newPos = function() {
        this.x += speedX;
        this.y += speedY;
    }
}

function updateGameArea(){
    myGameArea.clear();
    myGamePiece.newPos();
    myGamePiece.update();
}

function moveup(){
    myGamePiece.speedY -= 1;
}
function movedown(){
    myGamePiece.speedY += 1;
}
function moveright(){
    myGamePiece.speedX += 1;
}
function moveleft(){
    myGamePiece.speedX -= 1;
}



    </script>

    <button onmousedown="moveup()">UP</button>
    <button onmousedown="movedown()">DOWN</button>
    <button onmousedown="moveright()">RIGHT</button>
    <button onmousedown="moveleft()">LEFT</button>

</body>
</html>

Thank you for any help you can give!

Solution

 this.newPos = function() {
    this.x += speedX;
    this.y += speedY;

The console is correct, speedX and speedY do not exist.

There are three solutions:

Solution 1: Use that

var that = this; // Save a local copy of this

 this.newPos = function() {
    that.x += that.speedX;
    that.y += that.speedY;
 }

Solution 2: Use bind:

this.newPos = function() {
     this.x += this.speedX;
     this.y += thisspeedY;
}.bind(this);

Solution 3: ES6 - Use arrow functions

this.newPos = () => {
     this.x += this.speedX;
     this.y += thisspeedY;
 };