Here is the code for an exportStyles()
method that should return a CSS string including all inline and external styles for a given element, except default values (which was the main difficulty).
For example: console.log(someElement.exportStyles());
Since you are using Chrome, I did not bother making it compatible with IE.
Actually it just needs that the browsers supports the getComputedStyle(element)
method.
Element.prototype.exportStyles = (function () {
// Mapping between tag names and css default values lookup tables. This allows to exclude default values in the result.
var defaultStylesByTagName = {};
// Styles inherited from style sheets will not be rendered for elements with these tag names
var noStyleTags = {"BASE":true,"HEAD":true,"HTML":true,"META":true,"NOFRAME":true,"NOSCRIPT":true,"PARAM":true,"SCRIPT":true,"STYLE":true,"TITLE":true};
// This list determines which css default values lookup tables are precomputed at load time
// Lookup tables for other tag names will be automatically built at runtime if needed
var tagNames = ["A","ABBR","ADDRESS","AREA","ARTICLE","ASIDE","AUDIO","B","BASE","BDI","BDO","BLOCKQUOTE","BODY","BR","BUTTON","CANVAS","CAPTION","CENTER","CITE","CODE","COL","COLGROUP","COMMAND","DATALIST","DD","DEL","DETAILS","DFN","DIV","DL","DT","EM","EMBED","FIELDSET","FIGCAPTION","FIGURE","FONT","FOOTER","FORM","H1","H2","H3","H4","H5","H6","HEAD","HEADER","HGROUP","HR","HTML","I","IFRAME","IMG","INPUT","INS","KBD","KEYGEN","LABEL","LEGEND","LI","LINK","MAP","MARK","MATH","MENU","META","METER","NAV","NOBR","NOSCRIPT","OBJECT","OL","OPTION","OPTGROUP","OUTPUT","P","PARAM","PRE","PROGRESS","Q","RP","RT","RUBY","S","SAMP","SCRIPT","SECTION","SELECT","SMALL","SOURCE","SPAN","STRONG","STYLE","SUB","SUMMARY","SUP","SVG","TABLE","TBODY","TD","TEXTAREA","TFOOT","TH","THEAD","TIME","TITLE","TR","TRACK","U","UL","VAR","VIDEO","WBR"];
// Precompute the lookup tables.
for (var i = 0; i < tagNames.length; i++) {
if(!noStyleTags[tagNames[i]]) {
defaultStylesByTagName[tagNames[i]] = computeDefaultStyleByTagName(tagNames[i]);
}
}
function computeDefaultStyleByTagName(tagName) {
var defaultStyle = {};
var element = document.body.appendChild(document.createElement(tagName));
var computedStyle = getComputedStyle(element);
for (var i = 0; i < computedStyle.length; i++) {
defaultStyle[computedStyle[i]] = computedStyle[computedStyle[i]];
}
document.body.removeChild(element);
return defaultStyle;
}
function getDefaultStyleByTagName(tagName) {
tagName = tagName.toUpperCase();
if (!defaultStylesByTagName[tagName]) {
defaultStylesByTagName[tagName] = computeDefaultStyleByTagName(tagName);
}
return defaultStylesByTagName[tagName];
}
return function exportStyles() {
if (this.nodeType !== Node.ELEMENT_NODE) {
throw new TypeError("The exportStyles method only works on elements, not on " + this.nodeType + " nodes.");
}
if (noStyleTags[this.tagName]) {
throw new TypeError("The exportStyles method does not work on " + this.tagName + " elements.");
}
var styles = {};
var computedStyle = getComputedStyle(this);
var defaultStyle = getDefaultStyleByTagName(this.tagName);
for (var i = 0; i < computedStyle.length; i++) {
var cssPropName = computedStyle[i];
if (computedStyle[cssPropName] !== defaultStyle[cssPropName]) {
styles[cssPropName] = computedStyle[cssPropName];
}
}
var a = ["{"];
for(var i in styles) {
a[a.length] = i + ": " + styles[i] + ";";
}
a[a.length] = "}"
return a.join("\r\n");
}
})();
This code is base on my answer for a slightly related question: Extract the current DOM and print it as a string, with styles intact