Edit in JSFiddle

Result
JavaScript
HTML
CSS

x = 0;
y = 0;
speed = 5;
angle = 0;
mod = 0;

canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
car = new Image();
car.src = "http://i.imgur.com/uwApbV7.png";

window.addEventListener("keydown", keypress_handler, false);
window.addEventListener("keyup", keyup_handler, false);

var moveInterval = setInterval(function () {
    draw();
}, 30);

function draw() {
    context = canvas.getContext("2d");
    context.clearRect(0, 0, 800, 800);

    context.fillStyle = "rgb(200, 100, 220)";
    context.fillRect(50, 50, 100, 100);

    x += (speed * mod) * Math.cos(Math.PI / 180 * angle);
    y += (speed * mod) * Math.sin(Math.PI / 180 * angle);

    context.save();
    context.translate(x, y);
    context.rotate(Math.PI / 180 * angle);
    context.drawImage(car, -(car.width / 2), -(car.height / 2));
    context.restore();
}

function keyup_handler(event) {
    if (event.keyCode == 87 || event.keyCode == 83) {
        mod = 0;
    }
}

function keypress_handler(event) {
    console.log(event.keyCode);
    if (event.keyCode == 87) {
        mod = 1;
    }
    if (event.keyCode == 83) {
        mod = -1;
    }
    if (event.keyCode == 65) {
        angle -= 5;
    }
    if (event.keyCode == 68) {
        angle += 5;
    }
}

<body>
     <h1>WASD To Move</h1>

    <canvas id="canvas" width="800" height="800"></canvas>
</body>

#canvas {
    border: 2px solid #333;
}