Generates all permutations of a string (contains duplicates).

⚠️ WARNING: This function’s execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your browser to hang as it tries to solve all the different combinations.

Use recursion.
For each letter in the given string, create all the partial permutations for the rest of its letters.
Use Array.prototype.map() to combine the letter with each partial permutation, then Array.prototype.reduce() to combine all permutations in one array.
Base cases are for string length equal to 2 or 1.

代码片段

const stringPermutations = str => {
  if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
  return str
    .split('')
    .reduce(
      (acc, letter, i) =>
        acc.concat(stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)),
      []
    );
};

使用样例

stringPermutations('abc'); // ['abc','acb','bac','bca','cab','cba']