How to place several elements randomly on page?

Question

I want to place several elements of one class randomly on the page with Javascript / jQuery. My idea is to generate random values for margin-top, margin-left and z-index. The problem is that I need to generate values in between negative and positive (like from -150px to 300px) and I don't understand how to make it with the code I use:

$(".randomnumber").each(function () {
    var randomtop = Math.floor(Math.random() * 101);
    var randomleft = Math.floor(Math.random() * 101);
    var randomzindex = Math.floor(Math.random() * 101);
    $(this).css({
        "margin-top": randomtop,
        "margin-left": randomleft,
        "z-index": randomzindex
    });
});

http://jsfiddle.net/7JGqZ/651/

So the problems I have:

1. Don't know how to make it work with negative values — for example I need the top-margin to be from -150px to 300px.

2. The elements in the fiddle beave a bit strange, like their positions are not really random or like they're connected to each other...

Update:

Made it work, but still don't like the result, I actually would like elements to be placed randomly so they would fit the page size, I mean that elements would be placed all over the page, not going too far above the edge of the page. Now I have a parent element that is fixed in the centre of the page (has width and height = 0, top and bottom = 50%), and my idea was to position its child elements with generating top and left margins somehow like this:

$(document).ready(function(){
    $(".mood-img").each(function () {
        var height = $(window).height();
        var halfheight = height/2;
        var margintop = halfheight-400;
        var width = $(window).width();
        var halfwidth = width/2;
        var marginleft = halfwidth-500;
        var randomtop = getRandomInt(halfheight, margintop);
        var randomleft = getRandomInt(halfwidth, marginleft);
        var randomzindex = getRandomInt(1, 30);


        $(this).css({
            "margin-top": randomtop,
            "margin-left": randomleft,
            "z-index": randomzindex
        });
    });

    function getRandomInt(min, max) {
        return Math.floor(Math.random() * (max - min + 1) + min);
    }
});

http://jsfiddle.net/7JGqZ/657/

Answer 1

As for #1, you could generate a random number from 0 to 450 then subtract 150

$(".randomnumber").each(function () {
    var randomtop = Math.floor(Math.random() * 450 - 150);
    var randomleft = Math.floor(Math.random() * 450 - 150);
    var randomzindex = Math.floor(Math.random() * 450 - 150);
    $(this).css({
        "margin-top": randomtop,
        "margin-left": randomleft,
        "z-index": randomzindex
    });
});

Updated jsFiddle

If you want the elements to be randomly placed throughout the entire screen without overlapping the edges, you can use the following instead: Demo (I cleaned it up a bit too)

As for #2, there is no true random when it comes to coding. Most randoms, like Math.random are derived from the time. From Mozilla:

Returns a pseudo-random number in the range [0,1) — that is, between 0 (inclusive) and 1 (exclusive). The random number generator is seeded from the current time, as in Java.

The numbers are as random as possible in javascript. Google more information and alternates if you don't believe me

To demonstrate how well Math.random works, I edited the project to allow any number of element, set by numElems. Try it a few times, it works pretty well. Demo here

EDIT

I'd also recommend using scrollHeight and scrollWidth as opposed to using jQuery's width() and height() because it is more inclusive, thus giving a more accurate top value