To push a data into state array in ReactJS you can make use of the "useState()" hook and extract the previous data (usually using array destructure) and merge it together with the new data.
React Hooks Example
const [posts, setPosts] = useState([]);
To push value at the end of the array you can define your code like below.
setArray(oldPosts => [...oldPosts, newPost]);
To push value at the begging of the array you can just set the placement of the variable.
setArray(oldPosts => [newPost, ...oldPosts]);
