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

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']));

function 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());
// 

const lf = new Intl.ListFormat('en');
lf.format(['Frank']);
// → 'Frank'
lf.format(['Frank', 'Christine']);
// → 'Frank and Christine'
lf.format(['Frank', 'Christine', 'Flora']);
// → 'Frank, Christine, and Flora'
lf.format(['Frank', 'Christine', 'Flora', 'Harrison']);
// → 'Frank, Christine, Flora, and Harrison'

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));

let arrayToCustomStr = (arr, enableMutate) =>

 // Clone the received array (if required).
 let a = enableMutate ? arr : arr.slice(0);

 // Convert the array to custom string.
 let removed = a.splice(-2, 2);
 a.push(removed.join(" and "));
 return a.join(", ");


// First example, mutate of original array is disabled.
let input1 = ['one', 'two', 'three', 'four'];
console.log("Result for input1:" , arrayToCustomStr(input1));
console.log("Original input1:", input1);

// Second example, mutate of original array is enabled.
let input2 = ['one', 'two'];
console.log("Result for input2:", arrayToCustomStr(input2, true));
console.log("Original input2:", input2);

// Third example, lenght of array is 1.
let input3 = ['one'];
console.log("Result for input3:", arrayToCustomStr(input3));

// Fourth example, empty array.
let input4 = ;
console.log("Result for input4:", arrayToCustomStr(input4));

// Plus example.
let bob = [
 "Don't worry about a thing",
 "Cause every little thing",
 "Gonna be all right",
 "Saying, don't worry about a thing..."
];
console.log("Result for bob:", arrayToCustomStr(bob));

.as-console-wrapper 
 top: 0px;
 max-height: 100% !important;