// Add and remove array items with concat() and slice() 

// ...to avoid mutation

​

const letters = ['A', 'B', 'C', 'D'];

​

function append(array, value) {

  return [...array, value];

}

​

function prepend(array, value) {

  return [value, ...array];

}

​

function insertAt(array, index, value) {

  return [

    ...array.slice(0, index),

    value,

    ...array.slice(index)

  ];

}

​

function removeAt(array, index) {

  return [

    ...array.slice(0, index),

    ...array.slice(index + 1)

  ];

}

​

console.clear();

console.log('letters: ' + letters.join(', '));

console.log('append: ' + append(letters, 'append me').join(', '));

console.log('prepend: ' + prepend(letters, 'prepend me').join(', '));

console.log('insertAt: ' + insertAt(letters, 2, 'insertAt me').join(', '));

console.log('removeAt: ' + removeAt(letters, 1).join(', '));

console.log('letters: ' + letters.join(', '));

​