Refactor the snippet below so the call passes the array via the spread operator (...nums) instead of indexing each element manually.

Examples

Example 1:

Input:
const sum = (a, b, c) => a + b + c;
const nums = [4, 5, 6];
sum(nums[0], nums[1], nums[2]);
Output: 15
Explanation: spread expands the array into positional arguments at call time.

Given const sum = (a, b, c) => a + b + c; and const nums = [4, 5, 6];, write the pre-ES6 equivalent of calling sum with the array's elements spread into positional arguments, using Function.prototype.apply(null, nums). Explain why apply was the only option before the spread operator and why it is still occasionally useful.

Examples

Example 1:

Input:
const sum = (a, b, c) => a + b + c;
const nums = [4, 5, 6];
sum.apply(null, nums);
Output: 15
Explanation: apply's second argument is an array of positional args, achieving the same spread effect.

Define a sum function that accepts ANY number of arguments using rest parameters (...nums). The function should return the total of its inputs. Demonstrate it called with 3, 5, and 0 arguments.

Examples

Example 1:

Input: sum(1, 2, 3, 4, 5)
Output: 15
Explanation: rest collects all positional args into an array.

Example 2:

Input: sum()
Output: 0
Explanation: empty rest array reduces to 0 with an initial value.

Show how to merge three arrays into one using the spread operator, and contrast with Array.prototype.concat. Which approach is shorter and when does each one shine?

Examples

Example 1:

Input:
const a = [1, 2], b = [3, 4], c = [5];
[...a, ...b, ...c]
Output: [1, 2, 3, 4, 5]
Explanation: spread expands each array in place.