StackOverflow 18647552

HTML

<div id='circle'></div>

CSS

#circle {
    height:50px;
    width:50px;
    background:teal;
    -webkit-animation: stuff 1s infinite alternate;
}
@-webkit-keyframes stuff {
    100% {
        -webkit-transform: scale(2)
    }
}

JavaScript

onLoad("stuff");

function onLoad(anim) {
    var keyframes = findKeyframesRule(anim);
    alert(keyframes.cssRules.length);
}

function findKeyframesRule(rule) {
    var ss = document.styleSheets;
    console.log(ss);
    for (var i = 0; i < ss.length; ++i) {
        for (var j = 0; j < ss[i].cssRules.length; ++j) {
            if (ss[i].cssRules[j].type == window.CSSRule.WEBKIT_KEYFRAMES_RULE && ss[i].cssRules[j].name == rule) {
                return ss[i].cssRules[j];
            }
        }
    }
    return null;
}