Read CSS rule values with JavaScript

getStyle.js

import getStyle from  "./getStyleContent"; //ES6

let styleContent = getStyle('.test');

console.log(styleContent);

/* 
  Returns:
  
  .test {
     color: #000000;
     background-color: #fff;
   }
*/

getStyleContent.js

export default (styleName) => {
  for (let y = 0; y < document.styleSheets.length; y++) {
    let styles = document.styleSheets[y].rules || document.styleSheets[y].cssRules;
    for (let i = 0; i < styles.length; i++)
        if (styles[i].selectorText == styleName)
            return (styles[i].cssText ? styles[i].cssText : styles[i].style.cssText);
  }
  return false;
}