ATTENTION: This is not to find the rules of a specific element/node, this is to find if a combination of rules can be applied to any element.
I want to know if it's possible to determine with javascript if a combination of classes was defined in CSS.
For example, I want to know if ".some_class .small{some style}" combination was defined in CSS.
No JQuery please.
In fact you can only do this using native JS. jQuery does not support methods to deal with CSS rules traversing. Firstly you have to loop through all the document.styleSheets, in each sheet, you have to loop through all the sheet.cssRules. Each CssRule has a property called selectorText, you can get this and compare against your rule text. However you need to care about the order of identifiers in the selector path here. Here is the demo code:
var rulesChecker = {
compactRuleText: function(text) {
return text.replace(/[.#][^ +~>]+/g,
function(m){
return m.split(/([.#][^.#]+)/).sort().join('');
})
.replace(/(\s*?[>+~]\s*|\s+?(?=\s))/g, function(m){
return m.trim();
});
},
ruleExistence : [],
init : function(){
var sheets = document.styleSheets;
for(var i = 0; i < sheets.length; i++){
var rules = sheets[i].cssRules || sheets[i].rules;
for(var j = 0; j < rules.length; j++){
var a = this.compactRuleText(rules[j].selectorText);
this.ruleExistence[a] = true;
}
}
},
ruleExists : function(ruleText) {
var key = this.compactRuleText(ruleText);
return (key in this.ruleExistence);
}
};
rulesChecker.init();
//your rule text, note about the extra spaces and how close the identifiers are ...
//this in fact should match the rule in the CSS code (which is normally written)
var ruleText = ".f+.a.b#e > .d .k";
//ruleText = ".c";
alert(rulesChecker.ruleExists(ruleText));
.a.b:not(.f.g:not(.k.j)). Dealing with nested rules like this is not easy (but solvable), you need more research on this. Also when it comes to nested rules like that, we cannot solve it using just RegExp.If you have such an element in your document:
elt = document.querySelector('.some_class .small');
Then check the rules which applied with
rules = window.getMatchedCSSRules(elt)
However, I think support for getMatchedCSSRules is spotty, and it's not a standard.
See Is it possible to find CSS rules from an HTML node via JavaScript?, copy CSS styles that apply to an element, Is it possible to find CSS rules from an HTML node via JavaScript?, Javascript - How to get all matching classes and selector from css files for an element, Find all CSS rules that apply to an element, etc.
If you really want to find just the definitions for a particular selector, rather than the rules that apply to a particular element, you'll have to scan the stylsheets, as a commenter mentioned. However, selectors can be written in multiple ways, so it's not easy. For instance, #foo.bar and .bar#foo are equivalent.
$(".some_class.small").length.