prefix

Prefixes a CSS property based on the current browser.

• Use Array.prototype.findIndex() on an array of vendor prefix strings to test if Document.body has one of them defined in its CSSStyleDeclaration object, otherwise return null.
• Use String.prototype.charAt() and String.prototype.toUpperCase() to capitalize the property, which will be appended to the vendor prefix string.

const prefix = prop => {
  const capitalizedProp = prop.charAt(0).toUpperCase() + prop.slice(1);
  const prefixes = ['', 'webkit', 'moz', 'ms', 'o'];
  const i = prefixes.findIndex(
    prefix =>
      typeof document.body.style[prefix ? prefix + capitalizedProp : prop] !==
      'undefined'
  );
  return i !== -1 ? (i === 0 ? prop : prefixes[i] + capitalizedProp) : null;
};

prefix('appearance');
// 'appearance' on a supported browser, otherwise 'webkitAppearance', 'mozAppearance', 'msAppearance' or 'oAppearance'