<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
var arr1 = [1,2,3,4,5];
var arr2 = [6,7,8]
var res = arr1.concat(arr2);
console.log(res); //[1,2,3,4,5,6,7,8]
</script>
</body>
</html>