Javascript push on a localStorage item

Question

I tried too many question solutions from stack overflow but still i can't solve this issue and i have no idea where i'm going wrong this thing as i'm new to JavaScript coding.

Here is the code:

function SaveFavMovie(id)
{

let movies = moviesData.movies;
let movieid = -1;
for (let i = 0; i < movies.length; i++) {
    if (movies[i].id === id) {
        movieid = id;
    }
}
if(!movieid) return;

var a = [];
a = JSON.parse(localStorage.getItem('moviedb'));
a.push(id); 
localStorage.setItem('moviedb', JSON.stringify(a));
return true;

Here is the error get from the above code

Uncaught TypeError: a.push is not a function
at Object.SaveFavMovie

This is the line it shows the error

a.push(tmp);

The webstore 'moviedb' is empty and trying to push data for first time.

Answer 1

 a = JSON.parse(localStorage.getItem('moviedb'));

If the entry does not exist in localStorage (yet), it cannot parse anything and will therefore set a to null . And thats not an array. So in the case that it is not stored yet, you might wanna take an array instead:

 JSON.parse(localStorage.getItem('moviedb')) || [];