我用javascript写了这个函数，它应该在数组中添加和删除对象，并提醒它正在这样做。

function modifyWatchlist(id, boolean, array)  {
    const isAdding = boolean
    const targetMovie = array.filter(movie => movie.imdbID === id)
    const isRepeated = watchlist.find(movie => movie.imdbID === id)
    
    if (isAdding && isRepeated != undefined) {
        alert('Film already in your watchlist')
    } 
    else if (isAdding && isRepeated === undefined) {
        // watchlist.push(targetMovie[0])
        // localStorage.setItem('watchlist', JSON.stringify(watchlist))
        alert('Film added to your watchlist')
    }
    else if (!isAdding) {
        // const newWatchlist = watchlist.filter(movie => movie.imdbID !== id)
        // localStorage.setItem('watchlist', JSON.stringify(newWatchlist))
        alert('Film removed from your watchlist')
    }   
}

当运行上面的代码时，alert('Film already in your watchlist')语句甚至在isAdding === false时也运行。我不理解这背后的逻辑，也找不到修复它的方法。alert('Film removed from your watchlist')语句仍然按预期工作，但alert('Film already in your watchlist')总是先运行。
这是调用函数的一种方式：

document.addEventListener('click', (e) => {
    const id = e.target.dataset.id
    if (id) {
        modifyWatchlist(id, true, currentMovies)
    }
    else if (e.target.id === 'search-btn') {
        e.preventDefault()
        getMoviesArray()
    }
})

这是调用此函数的另一种方式

document.addEventListener('click', (e) => {
                const id = e.target.dataset.id
                if (e.target.dataset.id) {
                    modifyWatchlist(id, false, watchlist)
                    initWatchlist()
                }
            })