Permutations of a String in JavaScript

stringPermutation.js

// returns an array containing all permutations of a given string
const permute = str => {
  let permutations = [];

  if ( str.length <= 1 ) {
    return [str];
  }

  for ( let i = 0; i < str.length; i++ ) {
    let char = str[i];

    // if more than one occurence of the character
    if ( str.indexOf(char) !== i ) {
      continue;
    }

    let restOfString = str.slice(0, i) + str.slice(i + 1);
    permute(restOfString).forEach(item => {
      permutations.push(char + item);
    });
  }

  return permutations;
}