Javascript drag and drop series of articles 2

Some parameters related to positioning used in Javascript dragging

Before reading this article, please take a look at the offsetParent attribute in the first article of the Javascript drag and drop series article 1, because step by step is a good habit and worth promoting.
Okay, let’s take a look at what we have today.
First let’s take a look at the element.offsetLeft property.
Supported browsers: Internet Explorer 4.0, Mozilla 1.0, Netscape 6.0, Opera 7.0, Safari 1.0
Definition: Returns a pixel value that represents the left edge of the current element to the left edge of the object returned by its offsetParent property offset.
Syntax:
leftDis = element.offsetLeft
There is a bug in the implementation of the offsetLeft attribute in Internet Explorer. Regardless of the value of the offsetParent attribute of the current element, it always uses the Body element as a reference to calculate offsetLeft. Fortunately, this bug has been fixed in Internet Explorer 8 Beta 1. It is still important to note that IE will calculate OffsetLeft from the Left-Border of the Body element as the standard, while other browsers will calculate from Left-Margin.
Test code 1:
DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/ TR/html4/strict.dtd">
html>
 head>
 meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
 title>Untitled Documenttitle>
 style type="text/css">
body{
border:1px solid red;
margin-left :0px;
                                                  🎜 >{ position
:relative
;                left:25px;
                top:0px;
                border:1px solid black;

            }
        style>
        script type="text/javascript" language="JavaScript">
        function offset_init(){
            var pElement = document.getElementById("sonObj");
            parentObj = pElement.offsetParent;
            var ioffsetLeft=pElement.offsetLeft;

            alert(parentObj.tagName);
            alert(ioffsetLeft);
        }
        script>
    head>
    body onload="offset_init()">
        p id="parent">XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
        span id="sonObj">测试OffsetParent属性span>
        p>
body>
html>

In IE, after running this code, two windows will pop up in sequence, displaying "p" and "437" respectively, indicating offsetParent and offsetLeft respectively. In the picture below, the red border represents the Body element and the black border represents the p element. This proves that even in IE, offsetParent is not a Body element, and the calculation of offsetLeft is based on the Body element.

Figure 1: Result in IE7

This bug has been fixed in IE 8 Beta 1 and will return "p" and "411 respectively" ". Already compliant with the same standards as other browsers.

Figure 2: Test results of IE 8 Beta 1 in IETester

Note: IETester is a very good free web page test Tools that can render web pages on behalf of various versions of IE. The latest version 0.2.3 can be downloaded from its official website http://www.php.cn/. Personally, I think every WEB developer should have one.
It still needs to be noted that if you embed a label (as the current element) within an inline label (as an offsetParent), the code is as follows:

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX< ;p id="sonObj">Testing the OffsetParent property

will cause confusion because rendering varies from browser to browser (WebKit core browsers will The OffsetParent attribute will point to the Body element, and IE has different values ​​for OffsetLeft). When embedding inline tags within inline tags, the problem is particularly obvious (each browser has different values ​​for the OffsetLeft attribute, which is unreasonable). cycle).
Okay, we’ve finished talking about offsetLeft, let’s continue to look at the offsetTop attribute.
Supported browsers: Internet Explorer 4.0, Mozilla 1.0, Netscape 6.0, Opera 7.0, Safari 1.0
Definition:
Returns a value that specifies the distance from the top edge of the current element to the object returned by its offsetTop property distance from the upper edge.
Syntax:
topDis = element.offsetTop
The previous bug about offsetLeft also exists in the offsetTop attribute. Similarly, this bug has been fixed in IE 8 Beta 1.

Figure 3: Bug in the offsetsetTop attribute in IE7 and below.
Of course, do not embed tags inside inline tags, because WebKit kernel browsers will misinterpret the offsetParent attribute.
offsetWidth attribute
Supported browsers: Internet Explorer 4.0, Mozilla 1.0, Netscape 6.0, Opera 7.0, Safari 1.0
Definition:
The width of the current element.
Syntax:
elementWidth = element.offsetWidth
It should be pointed out that the width pointed by the offsetWidth attribute is the sum of the width padding border margin of the current element.
offsetHeight attribute
Supported browsers: Internet Explorer 4.0, Mozilla 1.0, Netscape 6.0, Opera 7.0, Safari 1.0
Definition:
The height of the current element.
Syntax:
elementHeight = element.offsetHeight
Similarly, the height pointed by the offsetWidth attribute is the sum of the Height padding border margin of the current element.
The four attributes mentioned above plus the offsetParent attribute in the previous article are actually not part of the Dom specification, but current browsers have implemented them. These attributes are also the core of realizing the Javascript drag and drop function. element. So be sure to understand them thoroughly.