Are there any function on js that can take two characters from tow different var and put it together on one element of array

Question

for example
var x="a";
var y="b";
/*and i have array i wont to make the first location of it "ab"*/

Answer 1

var arr =[ ]
var x="a"
var y="b"
arr.push(x+y)

Answer 2

please I don't understand what you mean

Answer 3

but where i can define the location on array that i wont stor "ab"in it

Answer 4

i wont the
arr[5]="ab"
for exampl