CSSStyleDeclaration length Property

Return the number of styles set on the H1 element:

var elmnt = document.getElementsByTagName("h1")[0];
var x = style.length;

Description

The length property returns the number of style declarations set for the specified element.

Property
length	Yes	Yes	Yes	Yes	Yes

Return the length property:

element.style.length

DOM Version:	CSS Object Model
Return Value:	A Integer, representing the number of style declaration set for the element

Loop through all the element's style declarations:

for (i = 0; i < elmnt.style.length; i++) {
txt += elmnt.style.item(i)
}