Question

i specified a div with a ID of testBox:

<div id="testBox"></div>

and style it in the head section :

#testBox {
        background: red;
        width: 25px;
        height: 25px;
        left: 0;
        top: 0;
            }

then at the bottom of the body,i put the JS :

var box = document.getElementById("testBox");
        console.log(box.style.left);
        console.log(box.style.width);

use the FireBug in FireFox ,but it just tell me:

it’s an empty string….

But when i put the style infomation in the div tag like this:

<div id="testBox" style="background: red;width: 25px;height: 25px;"></div>

then the JS could do its work,retrieve all the information i want

so is this the only way to get the style information whit it all inline ,or i just miss something,after all i am just new to the JS and DOM ….

Answer 1

When you say box.id what is returned to you is the id attribute of the box element as declared in your html.

When you say box.style you are accessing a javascript object also created based on your markup.

Styling attributes that are not defined inline are not used when the dom-representation of the style attribute is created.

Here is an article which highlights this behaviour.

However, if you use a library like jQuery you can do

$(function(){alert($("#textBox").css("width"));});

and this will give you your css value.

UPDATE:

Thanks to AVD for pointing me in the right direction:
Here is a method which uses his solution but adds support for IE < 9:

var box = document.getElementById("testBox");
var style = window.getComputedStyle ? window.getComputedStyle(box) : box.currentStyle;

alert("Height : " + style["height"]);
alert("Width : " + style["width"]);
alert("Left : " + style["left"]);

Here is a fiddle.