Returns an array of strings from axis tickValues for a given axis
@param {Object} props: the props object
@param {String} axis: the current axis
@returns {Array} an array of strings
function getStringsFromAxes(props, axis) {
  const { tickValues, tickFormat } = props;
  let tickValueArray;
  if (!tickValues || (!Array.isArray(tickValues) && !tickValues[axis])) {
    tickValueArray = tickFormat && Array.isArray(tickFormat) ? tickFormat : [];
  } else {
    tickValueArray = tickValues[axis] || tickValues;
  }
  return tickValueArray.filter((val) => typeof val === "string");
}