在页面加载时使用JavaScript在父容器中垂直居中子div是不是设置位置？

Question

I am using JavaScript to vertically center a child div within a fluid container. I essentially accomplish this by calculating the height of the parent container and the height of the child div. I then absolutely positon the child div in the center of the parent div based on the height. The issue I am experiencing is that when the page loads, it does not set the position of the child div. I created a function out of this and call it when the window is resized so that when the viewport changes it recalculates dynamically. How would I go about initially setting this position on page load?

<div class="lead">
    <div class="message"></div>
</div>

var homepageLead = function () {
var lead = $('.lead'),
    message = $('.message'),
    lead_height = lead.height(),
    message_height = message.height(),
    lead_center = .5 * lead_height,
    message_center = .5 * message_height,
    center = (lead_center - message_center);    
message.css('bottom',center);
}
homepageLead();

$(window).resize(function () {
    homepageLead();
});

Answer 1

Try this fiddle: http://jsfiddle.net/nRRn6/

used css:

html, body {
   height:100%;
}
.lead {
   width:100%;
   height:100%;
   background:red;
   position:relative;
}
.message {
   width:120px;
   height:200px;
   background:yellow;
   position:absolute;  /* <---required*/
   left:0;             /* <---required*/
   bottom:0;           /* <---required*/
}

used html:

<div class="lead">
    <div class="message"></div>
</div>

used jQuery:

var homepageLead = function () {
    var lead = $('.lead'),
        message = $('.message'),
        lead_height = lead.height(),
        message_height = message.height(),
        lead_center = .5 * lead_height,
        message_center = .5 * message_height,
        center = (lead_center - message_center);
    return message.css('bottom', center);
};

$(function () {
    $(window).resize(function () {
        homepageLead();
    }).resize();
});