The Book of JavaScript, 2nd Edition

Making divs Move

The top property of a div's style dictates the vertical position of the div, and the left property determines the horizontal position. You can use these properties to move a div around the screen. For example, to position a div 500 pixels from the left border of the browser window, do this:

document.getElementById('myDiv').style.left = 500;

Adding an amount to the top or left attribute of a div's style will move it vertically or horizontally. If a div is 500 pixels from the left border of the window, and you add 5 to the left property, you will move the div to a position 505 pixels from the border. Unfortunately, adding numbers to the left and top properties is not straightforward, because most browsers will stick a px at the end ...