random position of divs in javascript

Question

I'm trying to make Divs to appear randomly anywhere on a webpage with javascript. So a div appears then disappears, then another div appears somewhere else on the page then disappears, then another div appears again in another random spot on the page then disappears, and so on. I'm not sure on how to generate random units in pixels or what technique to use to generate random positions.

How do I do that? Here's my code:

var currentDivPosition = myDiv.offset(),
    myDivWidth = myDiv.width(),
    myDivHeight = myDiv.height(),
            var myDiv = $('<div>'),
    finalDivPositionTop, finalDivPositionLeft;

myDiv.attr({ id: 'myDivId', class: 'myDivClass' }); // already defined with position: absolute is CSS file.

// Set new position     
finalDivPositionTop = currentDivPosition.top + Math.floor( Math.random() * 100 );
finalDivPositionLeft = currentDivPosition.left + Math.floor( Math.random() * 100 );

myDiv.css({ // Set div position
  top: finalDivPositionTop,
  left: finalDivPositionLeft
});

$('body').append(myDiv);

myDiv.text('My position is: ' + finalDivPositionTop + ', ' + finalDivPositionLeft); 

myDiv.fadeIn(500);

setTimeout(function(){

  myDiv.fadeOut(500);

  myDiv.remove();       

}, 3000);

Answer 1

Here's one way to do it. I'm randomly varying the size of the div within a fixed range, then setting the position so the object is always placed within the current window boundaries.

(function makeDiv(){
    // vary size for fun
    var divsize = ((Math.random()*100) + 50).toFixed();
    var color = '#'+ Math.round(0xffffff * Math.random()).toString(16);
    $newdiv = $('<div/>').css({
        'width':divsize+'px',
        'height':divsize+'px',
        'background-color': color
    });

    // make position sensitive to size and document's width
    var posx = (Math.random() * ($(document).width() - divsize)).toFixed();
    var posy = (Math.random() * ($(document).height() - divsize)).toFixed();

    $newdiv.css({
        'position':'absolute',
        'left':posx+'px',
        'top':posy+'px',
        'display':'none'
    }).appendTo( 'body' ).fadeIn(100).delay(1000).fadeOut(500, function(){
      $(this).remove();
      makeDiv(); 
    }); 
})();

Edit: For fun, added a random color.

Edit: Added .remove() so we don't pollute the page with old divs.

Example: http://jsfiddle.net/redler/QcUPk/8/

Answer 2

Let's say you have this HTML:

<div id="test">test div</div>

And this CSS:

#test {
    position:absolute;
    width:100px;
    height:70px;
    background-color:#d2fcd9;
}

Using jQuery, if you use this script, whenever you click the div, it will position itself randomly in the document:

$('#test').click(function() {
    var docHeight = $(document).height(),
        docWidth = $(document).width(),
        $div = $('#test'),
        divWidth = $div.width(),
        divHeight = $div.height(),
        heightMax = docHeight - divHeight,
        widthMax = docWidth - divWidth;

    $div.css({
        left: Math.floor( Math.random() * widthMax ),
        top: Math.floor( Math.random() * heightMax )
    });
});

The way this works is...first you calculate the document width and height, then you calculate the div width and height, and then you subtract the div width from the document width and the div height from the document height and consider that the pixel range you're willing to put the div in (so it doesn't overflow out of the document). If you have padding and border on the div, you'll need to account for those values too. Once you've figured out the range, you can easily multiple that by Math.random() and find the random position of your div.

So once more: first find the dimensions of the container, then find the dimensions of your element, then subtract element dimensions from container dimensions, and THEN use Math.random() on that value.

The basic idea is encapsulated here:

http://jsfiddle.net/5mvKE/