findTargetSumWays = (nums, target, index = 0, sum = 0) => {
    const isBaseCase = (index === nums.length);
    if (isBaseCase) {
        const isTarget = (sum === target);
        if (isTarget) return 1;

        return 0;
    }

    return dfs(nums, target, index, sum);/* Time O(2^N) | Space O(HEIGHT) */
}
Brute Force - DFS
Time O(2^N) | Space O(N)
https://leetcode.com/problems/target-sum/
@param {number[]} nums
@param {number} target
@return {number}