Is there a way to find all the global styles that apply to a web page?

user_687677 0
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As a company, we use components (Angular, Vue and React) to build our applications, but we still have a good number of global styles that we inherited from our legacy app.

eg:

.active {
  background: red;
}

Will apply to any element anywhere on the page that has a class of active.

Is there a way, in the browser, to generate a list of all the global (i.e. non-namespaced) style rules that apply to a page, bearing in mind that these might be present inside of third-party libraries, or other miscellaneous legacy JavaScripts?

css javascript
4 Answers

The only option for evaluating the current page's CSS styles is to use document.styleSheets. It will return a list of CSSStyleSheets.

You will want to focus on document.styleSheets[n].cssRules, where n equals which stylesheet you want to evaluate. That will give you a list of all the styles applied by that stylesheet. Each stylesheet will have a cssText and a selectorText property.

If you just want to loop through to find which styles are 'non-namespaced' you should probably just use the selectorText properties.

Here is some more information on MDN about document.styleSheets.

Here is an example (press 'Run code snippet' to see results): 

var selectors = [];

var sheets = Array.from(document.styleSheets);

sheets.forEach(function(sheet) {
  // Only Stylesheets from a same-origin domain expose `cssRules` for security reasons
  try {
    var rules = Array.from(sheet.cssRules);
    rules.forEach(function(rule) {
      selectors.push(rule.selectorText);
    });
  } catch (e) {
    // Do something with external stylesheets if you want
  }
});

console.log(selectors);
<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>Stylesheets</title>
  <style>
    .hello-world {
      background: url(none.gif);
    }
  </style>
  <!-- Won't work as it is not a same-original stylesheet -->
  <link href="https://cdnjs.cloudflare.com/ajax/libs/normalize/3.0.2/normalize.min.css" rel="stylesheet" type="text/css" />
</head>

<body>
  <style>
    .foo {
      background: url(none.gif)
    }
    
    .bar {
      background: url(none.gif);
    }
  </style>
</body>

</html>

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