What I need to do is use selectpicker('refresh'). The Javascript now looks like this:
var select = document.getElementById("options");
select.innerHTML += "<option>two</option>"
$('.selectpicker').selectpicker('refresh');
So to dynamically create options in Javascript, I can do this:
function createOptions(options){
console.log(options) // ['one', 'two', 'three']
var select = document.getElementById("options");
select.innerHTML = "<option>"+options[0]+"</option>"
for(let i = 1; i < options.length; i++){
select.innerHTML += "<option>"+options[i]+"</option>"
}
// USE THIS TO RELOAD THE LIST \/ \/ \/
$('.selectpicker').selectpicker('refresh');
}