my solution for Word Search II problem (https://leetcode.com/problems/word-search-ii/). Probably has gigantic time complexity, so I'm 90% sure you can optimize the heck of it.

word-search-ii.js

function* anf(length, base) {
	let arr = new Array(length).fill(0);

	while (true) {
		yield arr;

		let br = true;
		for (let i = 0; i < length; i++) {
			if (arr[i] != base - 1) {
				++arr[i];
				br = false;
				break;
			} else {
				arr[i] = 0;
			}
		}
		if (br)
			break;
	}
}

/**
 * @param {character[][]} board
 * @param {string[]} words
 * @return {string[]}
 */
function findWords(board, words) {
	const
		m = board.length,
		n = board[0].length,
		max = words.reduce((acc, cur) => Math.max(acc, cur.length), 0);
	words = new Set(words);
	let ret = new Set;

	for (let y = 0; y < m; y++)
	for (let x = 0; x < n; x++) {
		for (let l = 0; l < max; l++) {
			for (let walks of anf(l, 4)) {
				// check if valid, also construct coords
					let walksCoords = new Array(l);
					let
						valid = true,
						mx = x, my = y;

					walksCoords[0] = [mx, my];
					for (let i = 0; i < l; i++) {
						// step
						switch (walks[i]) {
							case 0:
								--mx;
								break;
							case 1:
								++mx;
								break;
							case 2:
								--my;
								break;
							default:
								++my;
								break;
						}

						// check
						if (
							walksCoords.some(v => v[0] == mx && v[1] == my) ||  // check if coord exists
							!(0 <= mx && mx < n && 0 <= my && my < n)  // check if out of bounds
						) {
							valid = false;
							break;
						}

						// push
						walksCoords[i + 1] = [mx, my];
					}

				if (valid) {
					// construct string from walks
						let str = '';
						for (let i = 0; i < l + 1; i++)
							str += board[walksCoords[i][1]][walksCoords[i][0]];

					// check if in words
						if (words.has(str)) {
							ret.add(str);
						}
				}
			}
		}
	}

	return [...ret];
}

let
	board = [
		["o","a","a","n"],
		["e","t","a","e"],
		["i","h","k","r"],
		["i","f","l","v"]
	],
	words = ["oath","pea","eat","rain"];
findWords(board, words);