Use keypress
event on usersSearch
textbox and look for Enter button. If enter button is pressed then trigger the search button click event which will do the rest of work. Try this.
$('document').ready(function(){
$('#searchButton').click(function(){
var search = $('#usersSearch').val();
$.post('../searchusers.php',{search: search},function(response){
$('#userSearchResultsTable').html(response);
});
})
$('#usersSearch').keypress(function(e){
if(e.which == 13){//Enter key pressed
$('#searchButton').click();//Trigger search button click event
}
});
});