请问老师categories.map报错怎么解决?

TypeError: categories.map is not a function

  12 |                 <div className="row">
  13 |                     {
> 14 |                         categories.map((category, index) => {
     |                                    ^
  15 |                             const activeClassName = (selectedCategory && selectedCategory.id === category.id) ?

‘category-item col-3 active’ : ‘category-item col-3’