author.js

displayAuthorData();
function displayAuthorData() {
 let arr = localStorage.getItem('bookData');
 if (arr == null) {
 data = [];
 } else {
 data = JSON.parse(arr);
 }
 let rows = '';
 const dup = data.map(v => v.author).filter((v, i, vIds) => {
 if (vIds.indexOf(v) !== i) {
 return true;
 }
 });
 const duplicates = data.filter(obj => dup.includes(obj.author));
 const arr1 = getUniqueListBy(data, 'author');
 arr1.forEach((item, index) => {
 rows += `<tr class = 'tr'>
 <td>${index + 1}</td>
 <td>${item.author}</td>
 <td>${bookNames(item['author'])}</td>
 <td><button onClick = 'deleteData(${index})'>Delete</button></td>
 </tr>`
 })
 var tbody = document.getElementById("authorTable");
 tbody.innerHTML = rows;
}
function getUniqueListBy(arr, key) {
 return [...new Map(arr.map(item => [item[key], item])).values()]
}
function bookNames(author) {
 const counts = data.filter(item => item['author'] === author).map(i => i.name)
 return counts.length;
}
function deleteData(a) {
 const arr = getUniqueListBy(data, 'author');
 let author = arr[a]['author'];
 const dele = data.filter(data => data.author !== author);
 localStorage.setItem('bookData', JSON.stringify(dele));
 displayAuthorData();
}