Add / remove item from array without mutaiton

without_mutation.js

const students = ['yoshie', 'hiroshie', 'lisa', 'johnny'];

const removeStudent = (students, index) => {
  return [
    ...students.slice(0, index), 
    ...students.slice(index + 1)
  ]
}

const addStudent = (students, index, newStudent) => {
  return [
    ...students.slice(0, index),
    newStudent,
    ...students.slice(index)
  ]
}

console.log(addStudent(students, 2, 'arima'));  // ["yoshie", "hiroshie", "arima", "lisa", "johnny"]
console.log(students);                          // ["yoshie", "hiroshie", "lisa", "johnny"]
console.log(removeStudent(students, 1));        // ["yoshie", "lisa", "johnny"]
console.log(students);                          // ["yoshie", "hiroshie", "lisa", "johnny"]