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Array: slice()

With slice you can copy a subarray from an array: 
let abcd = ['a', 'b', 'c', 'd'];
let ab = abcd.slice(0, 2);
let bc = abcd.slice(1, 3);
let bcd = abcd.slice(1, 4);
The first parameter specifies the start index (included) and the second parameter specifies the end index (excluded). The original array will not be modified.

Exercise

Write a function halve that copy the first half of an array. With an odd number of array elements, the middle element should belong to the first half.

Example: halve([1, 2, 3, 4]) should return [1, 2].
function halve(arr) {
  let halfLength = Math.ceil(arr.length / 2);
  return arr.slice(0, halfLength);
}

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