GenerateChances.js

const isUpper = (str) => str === str.toUpperCase();
const cloneArray = (arr) => [...arr];

const cloneAndUpdateArray = (arr, value, index) => {
  const newArr = cloneArray(arr);
  newArr.splice(index, 1, value);

  return newArr;
};

const genCharChances = (words, chances, index, upper = false) => {
  return chances.reduce((acc, cur) => {
    const value = upper ? cur.toUpperCase() : cur;
    const result = words.map((arr) => cloneAndUpdateArray(arr, value, index));
    return [...acc, ...result];
  }, []);
};

const genChances = (input, prox) => {
  return input
    .split("")
    .reduce((acc, cur, index, src) => {
      const chances = prox[cur.toLowerCase()]; || [cur]
      const words = [...acc, src];
      const result = genCharChances(words, chances, index, isUpper(cur));

      return acc.concat(result);
    }, [])
    .map((v) => v.join(""));
};

const result = genChances("pPp", { p: ["o", "l"] });
console.log("resultado", result);