JS error, finally found that the $(function () {}) part () is incomplete
$(function({
$("#directionSelect").change(function(){
$.ajax({
url:"",
success:function(data){
if(data.state=="fail"){
alert("The system is busy, please try again later!");
}else{
}
}
});
});
});
After summarizing the previous errors, it is found that most of the errors are incomplete symbols, such as missing a bracket or a quotation mark