JS c960 generator- https://repl.it/Dhqa/19

Dhqa-19.js

function c960seq (){
	var emptySquares = new Set([1,2,3,4,5,6,7,8]);
	var peiceMap = new Map()
	var ob = (Math.floor(Math.random() * 4)+1)*2-1;
	var eb = (Math.floor(Math.random() * 4)+1)*2;
	function pickasquare(){
		do{
			tsq = (Math.floor(Math.random() * 8)+1);
		}
		while (emptySquares.has (tsq)===false);
		return tsq;
	}
	function getblanksq(){
		tsq=0
		while (emptySquares.has (tsq)===false){
		tsq ++;	
}
		return tsq;
	}
    peiceMap.set(ob,"Bishop. ");
    peiceMap.set(eb,"Bishop. ");
    emptySquares.delete (eb);
    emptySquares.delete (ob);
    var ns1=pickasquare();
    peiceMap.set(ns1, "Knight. ");
    emptySquares.delete (ns1);
    var ns2=pickasquare();
    peiceMap.set(ns2, "Knight. ");
    emptySquares.delete (ns2);
    var qs=pickasquare();
    peiceMap.set(qs, "Queen. ");
    emptySquares.delete (qs);
	var rs1=getblanksq();
	peiceMap.set(rs1, "Rook. ");
	emptySquares.delete(rs1);
	var ks=getblanksq();
	peiceMap.set(ks, "King. ");
	emptySquares.delete(ks);
	var rs2=getblanksq();
	peiceMap.set(rs2, "Rook. ");
	emptySquares.delete(rs2);
	
	
	return (peiceMap.get(1)+peiceMap.get(2) +peiceMap.get(3)+peiceMap.get(4) +peiceMap.get(5)+peiceMap.get(6) +peiceMap.get(7)+peiceMap.get(8));
}