https://codepen.io/deusmorto/pen/YaJbPR

word-search.js

const cases = [
  "GROC",
  "FERNANDO",
  "GC",
  "AMIAT",
  "AML",
  "GABE",
  "GRMLAWE",
  "SLMIBE",
  "RMLAIB",
  "CORGAMLSTAIBEWZN",
  "GAGA",
  "CORGAMLSTAIBEWZS",
  "GMIAWZN",
  "ZALORG",
  "WIMLAZE",
  "WIMLAZ",
  "AAAABBBB",
  "WZNTSCORGABEWZN",
];

const sample = [
  ["G", "A", "B", "E"],
  ["R", "M", "I", "W"],
  ["O", "L", "A", "Z"],
  ["C", "S", "T", "N"],
];

const increase = (value) => value + 1;

const decrease = (value) => value - 1;

const get = (object) => (attribute) => object[attribute];

const normalize = (object) => String(object).toLowerCase().trim();

const indexColumnBy = (row) => (indexes, letter, column) => {
  const index = normalize(letter);
  const current = indexes[index];
  const coordinates = [[row, column]];
  const value = current ? current.concat(coordinates) : coordinates;

  return Object.assign(indexes, { [index]: value });
};

const indexRow = (indexes, letters, row) =>
  letters.reduce(indexColumnBy(row), indexes);

const getSiblings = ([row, column]) => [
  [decrease(row), column], // ⭡
  [decrease(row), increase(column)], // ↗
  [row, increase(column)], // ⭢
  [increase(row), increase(column)], // ↘
  [increase(row), column], // ⭣
  [increase(row), decrease(column)], // ↙
  [row, decrease(column)], // ⭠
  [decrease(row), decrease(column)], // ↖
];

const contains = (element) => ({
  at: (collection) => !!~collection.map(normalize).indexOf(normalize(element)),
});

const isSibiling =
  (reference = []) =>
  (coordinates) =>
    contains(coordinates).at(getSiblings(reference));

const walk = (stack, possibilities = []) => {
  const previous = possibilities.reverse().find(isSibiling(stack.previous));
  const invalid = !!previous && !contains(previous).at(stack.path);
  const valid = !stack.valid ? stack.valid : invalid;
  const path = !stack.valid ? stack.path : stack.path.concat([previous]);

  return { previous, valid, path };
};

const check = (tail) => (valid, head) => {
  const stack = { previous: head, valid: true, path: [head] };

  return valid || tail.reduce(walk, stack).valid;
};

const find = (matrix) => (word) => {
  const letters = normalize(word).split("");
  const indexes = matrix.reduce(indexRow, {});
  const getCoordinates = get(indexes);
  const head = letters.shift();
  const tail = letters.map(getCoordinates);
  const directions = getCoordinates(head);

  return !!directions && directions.reduce(check(tail), false);
};

const finder = find(sample);

const test = (word) => console.log(word, finder(word));

cases.forEach(test);