SOURCE

function permutate(str) {
    //保存每一轮递归的排列结果
    var result = [];
    //初始条件：长度为1
    if (str.length == 1) {
        return [str]
    } else {
        //求剩余子串的全排列,对每个排列进行遍历
        var preResult = permutate(str.slice(1));
        console.log('preResult', preResult)
        for (var j = 0; j < preResult.length; j++) {
            for (var k = 0; k < preResult[j].length + 1; k++) {
                //将首字母插入k位置  
                var temp = preResult[j].slice(0, k) + str[0] + preResult[j].slice(k);
              	console.log(str)
                result.push(temp);
            }
        }
        console.log('result', result)
        return result;
    }
}
permutate('1234')
console.log('4'.slice(1))