code: function keyMapper(mapper) {
    return obj => {
      if (!isObject(obj) || Array.isArray(obj)) {
        return obj;
      }
  
      const keys = Object.keys(obj);
      const out = {};
  
      for (let i = 0, l = keys.length; i < l; ++i) {
        const key = keys[i];
        out[mapper(key)] = obj[key];
      }
  
      return out;
    };
  }
docs: Returns a function that takes an object as an input and maps the object's keys using `mapper`. If the input is not an object, the input is returned unchanged.