Call concat() on the first array, and pass each array to merge with it in as arguments. It returns a new array.
var sandwiches1 = ['turkey', 'tuna', 'blt'];
var sandwiches2 = ['chicken', 'pb&j'];
var allSandwiches = sandwiches1.concat(sandwiches2);
// logs ['turkey', 'tuna', 'blt', 'chicken', 'pb&j']
console.log(allSandwiches);