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dojo.position

Status:Draft
Version:1.0
Available:since 1.4

Getter for the position and size of a DOM node.

Introduction

The dojo.position function is used to obtain position and size information about a DOM node. The type of information it returns is the width and height of the DOM node’s border-box (or borderStart-to-borderEnd size), and absolute position (border-start) in the form of x and y coordinates. If the optional includeScroll boolean parameter (default=false) has the value true, then the returned x and y values are offsets from the document root (unaffected by window scrolling), otherwise they are relative to the current viewport. The return object looks like:

{ w: 300: h: 150, x: 700, y: 900, }

for a node with a width of 300px and a height of 150px, with page absolute coordinates of 700px on the x-axis and 900px on the y-axis.

Usage Examples

Example 1: Center a small DOM node (with background image) over a larger DOM node (the frame) both vertically and horizontally relative to the document root

version:1.4-2.0
<script>
  var lastX = 0, lastY = 0;
  function doit(){
    var divInfo = dojo.position('div1', true), // use true to get the x/y relative to the document root
        span = dojo.byId('span1'),
        spanInfo = dojo.position(span, true);
    lastX += divInfo.x - spanInfo.x + (divInfo.w - spanInfo.w) / 2;
    lastY += divInfo.y - spanInfo.y + (divInfo.h - spanInfo.h) / 2;
    dojo.style(span, {
        left: lastX + "px",
        top: lastY + "px"
    });
  }
</script>
<span id="span1" class="centered" style=""></span>
<div id="div1" class="container" style=""></div>
<button type="button" onclick="doit()" class="">Click to center the image over the frame</button>
<style type="text/css">
  .container {
      background: url(http://docs.dojocampus.org/dojo/position?action=AttachFile&do=get&target=frame.png) no-repeat;
      width: 237px;
      height: 181px;
  }
  .centered {
      background: url(http://docs.dojocampus.org/dojo/position?action=AttachFile&do=get&target=img.png) no-repeat;
      width: 171px;
      height: 121px;
      position: absolute;
      left: 0;
      top: 0;
      border: 1px solid white;
  }
</style>

Comparison of various DOM node position/size methods

To see the effect of dojo.position’s includeScroll boolean parameter, scroll the window down and click the 15x120 content area.

version:1.4-2.0
<script type="text/javascript">
function compareMethods(){
    var testNode = dojo.byId('testNode'),
        contentBox = dojo.contentBox(testNode),
        marginBox = dojo.marginBox(testNode),
        position_win = dojo.position(testNode, true),
        position_view = dojo.position(testNode, false),
        coords_win = dojo.coords(testNode, true),
        coords_view = dojo.coords(testNode, false);
    for (var attr in {x:0,y:0,w:0,h:0,l:0,t:0}){
            for (var fcn in {position_win:0, position_view:0, marginBox:0, contentBox:0, coords_win:0, coords_view:0}){
                    var val = eval(fcn)[attr];
                    dojo.byId(fcn+"_"+attr).innerHTML = !isNaN(val)?val:"--";
            }
    }
}
dojo.addOnLoad(function(){
    compareMethods();
});
</script>
<fieldset style="display:inline;border:15px solid gray;border-width:15px 0 0 15px;margin:0px;padding:0px;font:14px monospace;background-color:white;outline:1px dotted black;">
    <fieldset style="display:inline;border:0px;border:0px;padding:0px;width:270px;height:165px;overflow:hidden;position:relative;left:-15px;top:-15px;">
            <div id="testNode" style="display:inline;margin:25px;border:20px solid gray;padding:30px;float:left;position:relative;left:15px;top:15px;" onclick="compareMethods()">
                    <center style="display:block;margin:0px;padding:0px;border:0px;width:120px;height:15px;background-color:gray;color:white;overflow:hidden;">15x120 content</center>
                    <nobr style="position:absolute;left:2px;top:2px;color:black;">padding 30px</nobr>
                    <nobr style="position:absolute;left:-18px;top:-18px;color:white;">border 20px</nobr>
                    <nobr style="position:absolute;left:-43px;top:-43px;color:black;">margin 25px</nobr>
                    <nobr style="position:absolute;left:-63px;top:-63px;color:white;">left/top 15px</nobr>
            </div>
    </fieldset>
</fieldset>
<table rules=all cellpadding=2 cellspacing=2 border=2 style="font:16px monospace;text-align:center;">
    <tr><td></td><td colspan="6">attribute</td></tr>
    <tr><td>function</td><td>x</td><td>y</td><td>w</td><td>h</td><td>l</td><td>t</td></tr>
    <tr><td style="text-align:left;">dojo.position(node,true)</td><td id="position_win_x"></td><td id="position_win_y"></td><td id="position_win_w"></td><td id="position_win_h"></td><td id="position_win_l"></td><td id="position_win_t"></td></tr>
    <tr><td style="text-align:left;">dojo.position(node,false)</td><td id="position_view_x"></td><td id="position_view_y"></td><td id="position_view_w"></td><td id="position_view_h"></td><td id="position_view_l"></td><td id="position_view_t"></td></tr>
    <tr><td style="text-align:left;">dojo.marginBox(node)</td><td id="marginBox_x"></td><td id="marginBox_y"></td><td id="marginBox_w"></td><td id="marginBox_h"></td><td id="marginBox_l"></td><td id="marginBox_t"></td></tr>
    <tr><td style="text-align:left;">dojo.contentBox(node)</td><td id="contentBox_x"></td><td id="contentBox_y"></td><td id="contentBox_w"></td><td id="contentBox_h"></td><td id="contentBox_l"></td><td id="contentBox_t"></td></tr>
    <tr style="color:gray;"><td style="text-align:left;">dojo.coords(node,true)</td><td id="coords_win_x"></td><td id="coords_win_y"></td><td id="coords_win_w"></td><td id="coords_win_h"></td><td id="coords_win_l"></td><td id="coords_win_t"></td></tr>
    <tr style="color:gray;"><td style="text-align:left;">dojo.coords(node,false)</td><td id="coords_view_x"></td><td id="coords_view_y"></td><td id="coords_view_w"></td><td id="coords_view_h"></td><td id="coords_view_l"></td><td id="coords_view_t"></td></tr>
</table>

Notes

  • Remember that page coordinates start as the top leftmost of the page is 0px, 0px
  • dojo.coords is deprecated starting in Dojo 1.4 since it’s a mixin of the much faster dojo.position and dojo.marginBox