code: function getComputedLength(value, element) {
  	var length = value.match(LENGTH_REGEXP);
  	if (!length) {
  		return parseFloat(value);
  	}
  	value = parseFloat(length[1]);
  	var unit = length[2].toLowerCase();
  	if (FIXED_UNIT_MAP[unit]) {
  		return value * FIXED_UNIT_MAP[unit];
  	}
  	if (unit === 'vw') {
  		return value * window.innerWidth / 100;
  	}
  	if (unit === 'vh') {
  		return value * window.innerHeight / 100;
  	}
  	if (unit === 'vmin') {
  		return value * Math.min(window.innerWidth, window.innerHeight) / 100;
  	}
  	if (unit === 'vmax') {
  		return value * Math.max(window.innerWidth, window.innerHeight) / 100;
  	}
  	// em units
  	if (unit === 'rem') {
  		element = documentElement;
  	}
  	if (unit === 'ex') {
  		value /= 2;
  	}
  	return parseFloat(getComputedStyle(element).fontSize) * value;
  }
docs: Get the computed length in pixel of a CSS length value
  
  @param  {string}  value
  @param  {Element} element
  @return {number}