Merge consecutive array elements

mergeConsecutiveElements.js

const last = a => a[a.length - 1];
const mergeConsecutive = (arr, el) => (arr.length <= 1) ?
    arr :
    arr.slice(1).reduce((p, v) => v === el && last(p) === v ?
        p :
        [...p, v], [arr[0]]);
const mergeConsecutiveElements = arr => (arr.length <= 1) ?
    arr :
    arr.slice(1).reduce((p, v) => last(p) === v ? p : [...p, v], [arr[0]]);