December 26, 2000 - Physical Measurements | WebReference

December 26, 2000 - Physical Measurements

Yehuda Shiran December 26, 2000
Physical Measurements
Tips: December 2000

Yehuda Shiran, Ph.D.
Doc JavaScript

The browser-independent W3C Standard's way to set and get an element's position is via the STYLE object's left and top properties. These properties denote physical measurements. Physical measurements are used either in HTML's STYLE attribute or in JavaScript. In HTML, they are numeric properties. Numeric properties comprised of a number, followed by units of measure. The following numeric properties are example values of the left and top properties: 50px, 32px, and 0px. Here is an example of specifying the STYLE attribute with numeric properties:

<INPUT ID="counter1" STYLE="position:relative; left:200px" TYPE="button" 
VALUE="Just a Button" onclick="handleClick()">

As JavaScript does not support the "numeric property" data type, these measurements become strings when you extract them into JavaScript variables. The string includes a number followed by the string "px". The following strings are example values of the left and top JavaScript variables: "50px", "32px", and "0px". When setting these properties in JavaScript, concatenate the "px" string to the value. For example, to set the left property of an element with ID="counter1" to xlocation, you will write:

document.getElementById('counter1').style.left = xlocation + "px";

The browser won't complain if you omit the "px" string:

document.getElementById('counter1').style.left = xlocation;

The browser assumes the unit of measure is pixels and will add the "px" automatically. You'll always get a "px"-ended string when querying the top and left properties.