Get a all combinations of array elements

Question

Example if a give A B C D i want get A AB AC ABCD B BA BC BD BACD BCAD BDAC BDCA...

i tried this code but this code is not given BCDA BCAD etc.

var letters = ["A", "B", "C", "D"] 

var combi = [];
var temp= "";

var letLen = Math.pow(2, letters.length);

for (var i = 0; i < letLen ; i++){
    temp= "";
    for (var j=0;j<letters.length;j++) {
        if ((i & Math.pow(2,j))){ 
        temp += letters[j]
        }
    }
    if (temp !== "") {
        combi.push(temp);
    }
}

console.log(combi.join("\n"));