JavaScript - 字符串全排列

给定字符串'abc'，输出该字符串的全排列。
['abc','acb','bac','bca','cba','cab']

递归实现：

function permutation (str) {
    let arr = [...str];
    let result = [];
    function loop(index) {
        if (index === arr.length - 1) {
            result.push([...arr].join(''));
            return;
        }
        for(let i = index; i < arr.length; i++) {
            [arr[index],arr[i]] = [arr[i],arr[index]];
            loop(index + 1);
            [arr[index],arr[i]] = [arr[i],arr[index]];            
        }
    }
    loop(0);
    return result;
}

console.log(permutation('abc'));
// [ 'abc', 'acb', 'bac', 'bca', 'cba', 'cab' ]