Join an array by commas and "and"

One option would be to pop the last item, then join all the rest by commas, and concatenate with and plus the last item:

const input = ['one', 'two', 'three', 'four'];
const last = input.pop();
const result = input.join(', ') + ' and ' + last;
console.log(result);

If you can't mutate the input array, use slice instead, and if there might only be one item in the input array, check the length of the array first:

function makeString(arr) {
  if (arr.length === 1) return arr[0];
  const firsts = arr.slice(0, arr.length - 1);
  const last = arr[arr.length - 1];
  return firsts.join(', ') + ' and ' + last;
}

console.log(makeString(['one', 'two', 'three', 'four']));
console.log(makeString(['one']));

You can use Array.prototype.slice() when array.length is bigger than 1 and exclude the rest of the cases:

const result = a => a.length > 1 
  ? `${a.slice(0, -1).join(', ')} and ${a.slice(-1)}` 
  : {0: '', 1: a[0]}[a.length];

Code example:

const input1 = ['one', 'two', 'three', 'four'];
const input2 = ['A Tale of Two Cities', 'Harry Potter and the smth', 'One Fish, Two Fish, Red Fish, Blue Fish'];
const input3 = ['one', 'two'];
const input4 = ['one'];
const input5 = [];

const result = a => a.length > 1 
  ? `${a.slice(0, -1).join(', ')} and ${a.slice(-1)}` 
  : {0: '', 1: a[0]}[a.length];

console.log(result(input1));
console.log(result(input2));
console.log(result(input3));
console.log(result(input4));
console.log(result(input5));

I like Mark Meyer's approach as it doesn't alter the input. Here's my spin:

const makeCommaSeparatedString = (arr, useOxfordComma) => {
  const listStart = arr.slice(0, -1).join(', ')
  const listEnd = arr.slice(-1)
  const conjunction = arr.length <= 1 
    ? '' 
    : useOxfordComma && arr.length > 2 
      ? ', and ' 
      : ' and '

  return [listStart, listEnd].join(conjunction)
}

console.log(makeCommaSeparatedString(['one', 'two', 'three', 'four']))
// one, two, three and four

console.log(makeCommaSeparatedString(['one', 'two', 'three', 'four'], true))
// one, two, three, and four

console.log(makeCommaSeparatedString(['one', 'two'], true))
// one and two

console.log(makeCommaSeparatedString(['one']))
// one

console.log(makeCommaSeparatedString([]))
//

Starting in V8 v7.2 and Chrome 72, you can use the sweet Intl.ListFormat API. It will also take care of localizing your list when requested, which might be of great help if you need it.

const lf = new Intl.ListFormat('en');

console.log(lf.format(['Frank']));
// → 'Frank'

console.log(lf.format(['Frank', 'Christine']));
// → 'Frank and Christine'

console.log(lf.format(['Frank', 'Christine', 'Flora']));
// → 'Frank, Christine, and Flora'

console.log(lf.format(['Frank', 'Christine', 'Flora', 'Harrison']));
// → 'Frank, Christine, Flora, and Harrison'

// You can use it with other locales
const frlf = new Intl.ListFormat('fr');

console.log(frlf.format(['Frank', 'Christine', 'Flora', 'Harrison']));
// → 'Frank, Christine, Flora et Harrison'

You can even specify options to make it a disruption and use "or" instead of "and", or to format units such as "3 ft, 7 in".

It's not very widely supported as of writing, so you might not want to use it everywhere.

References
The Intl.ListFormat API - Google Developers
V8 release v7.2

Tags:

Javascript

Arrays

String

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