CssParser.js

function CssParser()
{
    this.getSheetByHref = function(href) {
    // for external style sheet declared in <link> element, get definitions and return CSSStyleSheet object
        var sheet = null;                       // initialize to indicate failure
        var sheets = document.styleSheets;      // get array of all <link> and <style> objects
        var last = sheets.length;               // how many
        for (var i = 0; i < last; i++) {
            var s = sheets[i];                  // current sheet
            var h = s.href;                     // attempt to get href attribute
            // if href matches, parse filename and keep only that part of url
            if (h) h = h.substring(1 + s.href.lastIndexOf('/'));
            if (href == h) {        // if href of this sheet is that requested...
                sheet = s;          // assign current sheet as CSSStyleSheet object
                break;              // quit immediately, since target was found
            }
        }
        return sheet;   // return CSSStyleSheet (or null, if search failed)
    };
    this.getRules = function(sheet) {
        var rules = null;       // initialize to indicate failure
        if (null != sheet) {
            // if valid sheet, get rules by browser
            rules = (sheet.cssRules)?sheets.cssRules:sheets.rules
        }
        return rules;   // return rules (or null, if search failed)
    };
    this.getRule = function(selector, sheet) {
        // get rule, if sheet declares one for selector
        var rule = null;                        // initialize to indicate failure
        var rules = getRules(sheet);            // get rules for sheet
        if (null != rules) {
            var last = rules.length;            // how many
            for (var i = 0; i < last; i++) {    // for each rule
                // if selector matches capture and quit searching
                if (rules[i].selectorText == selector) rule = rules[i]
                break;
            }
        }
        return rule;    // return rule (or null, if search failed)
    };
    this.getAttributeValue = function(attribute, selector, sheet) {
        // get value of style attribute, if sheet declares one for selector
        var value = null;       // initialize to indicate failure
        // get value of attribute, if sheet declares one for selector
        var rule = getRule(selector, sheet);
        if (null != rule && rule.style && rule.style.cssText) {
            var attrValuePairs = rule.style.cssText;
            var startIdx = attrValuePairs.lastIndexOf(attribute);
            if (-1 != startIdx) {
                var avp = attrValuePairs.substring(startIdx)
                var stopIdx = avp.indexOf(';');
                if (-1 != stopIdx) {
                    var avp = avp.substring(0, avp.indexOf(stopIdx));
                    if (-1 != avp.indexOf(':')) {
                        value = avp.split(':')[1];
                    }
                }
            }
        }
        return value;   // return rule (or null, if search failed)
    };
};