const head = arr => (arr && arr.length ? arr[0] : undefined);

head([1, 2, 3]); // 1
head([]); // undefined
head(null); // undefined
head(undefined); // undefined

// `date` is a `Date` object
const formatYmd = date => date.toISOString().slice(0, 10);

// Example
formatYmd(new Date());      // 2020-05-06

const getSearchTerm = delimiter => {
	let searchTerm = "";

	for (let i = 1; i < commands.length - 1; i++)
	searchTerm = searchTerm + commands[i] + delimiter;

	searchTerm += commands[commands.length - 1];

	return searchTerm;
	};

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var productExceptSelf = function(nums) {
    var output = [];
    var leftMult = 1;
    var rightMult = 1;
    for (var i=nums.length - 1; i >= 0; i--) {
        output[i] = rightMult;
        rightMult *= nums[i];
        console.log({output: JSON.stringify(output), i})
    }
    for (var j=0; j < nums.length; j++) {
        output[j] *= leftMult;
        leftMult *= nums[j];
        console.log({output: JSON.stringify(output), j})
    }
    return output;
};

console.log(productExceptSelf([1, 2, 3, 4]))

console.log("xa")

const gcd = (...arr) => {
  const _gcd = (x, y) => (!y ? x : gcd(y, x % y));
  return [...arr].reduce((a, b) => _gcd(a, b));
};

gcd(8, 36); // 4
gcd(...[12, 8, 32]); // 4