permutation.js

function permutations(str) {
    let arr = []
    // base case: less than 2 characters in the string
    if (str.length < 2) {
        arr.push(str)
        return arr
    } 
    for (let i = 0; i < str.length; i++) {
        let currentChar = str[i]
        let remainingStr = str.slice(0, i) + str.slice(i + 1, str.length)
        let remainingPermutation = permutations(remainingStr) // save the result of the recursive function
        // if we find a repeating character, don't add it to the arr
        if (str.indexOf(currentChar) !== i) {
            continue
        }
        // concat currentChar with each substring and push to the arr
        remainingPermutation.forEach(subString => arr.push(currentChar + subString))
    }
    return arr
}