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List Format

Yangshun TayEx-Meta Staff Engineer
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Given a list of strings, implement a function listFormat that returns the items concatenated into a single string. A common use case is summarizing reactions on social media posts.

The function should support a few options as the second parameter:

  • sorted: Sorts the items alphabetically.
  • length: Shows only the first length items, using "and X other(s)" for the remaining. Ignore invalid values (negative, 0, etc.).
  • unique: Removes duplicate items.

Examples

listFormat([]); // ''


listFormat(['Bob']); // 'Bob'
listFormat(['Bob', 'Alice']); // 'Bob and Alice'


listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John']);
// 'Bob, Ben, Tim, Jane and John'


listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], {
  length: 3,
}); // 'Bob, Ben, Tim and 2 others'


listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], {
  length: 4,
}); // 'Bob, Ben, Tim, Jane and 1 other'


listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], {
  length: 3,
  sorted: true,
}); // 'Ben, Bob, Jane and 2 others'


listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John', 'Bob'], {
  length: 3,
  unique: true,
}); // 'Bob, Ben, Tim and 2 others'


listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], {
  length: 3,
  unique: true,
}); // 'Bob, Ben, Tim and 2 others'


listFormat(['Bob', 'Ben', '', '', 'John']); // 'Bob, Ben and John'

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    List Format | JavaScript Interview Questions with Solutions