ajax returning json data as undefined - html

Question

when i run below code.
it makes error and alert "fail error:StntaxError: Unexpected token < in JSON at position 0 data:undefined"
what is the problem ??
$("#a").click(function () {
st_dt = $("#st_dt").val();
end_dt = $("#end_dt").val();
lot_cd = $("#lot_cd").val();
var obj = { st_dt: st_dt, end_dt: end_dt, lot_cd: lot_cd };
var json_1 = JSON.stringify(obj);
$.ajax({
type: "POST",
url: '{{ url_for("get_operid") }}',
data: json_1,
dataType: "JSON",
success: function (data) {
alert("Success\n" + data);
},
error: function (request, status, error, data) {
alert("fail\n" + "error:" + error + "\n data:" + data);
}
});
});

Answer 1

Looking at the code it looks like a Laravel API request using Blade Template or the Function url_for is in Flask... In either case
That means the response for the api request is HTML string instead of
a json response...
i.e. The API request is returning a login page or some HTML page...
To check the response you can open the Chrome Devtools in the Network tab check the response of the API...

Answer 2

what you can try is :
var obj = { st_dt: st_dt, end_dt: end_dt, lot_cd: lot_cd };
console.log(obj);
var json_1 = JSON.stringify(obj);
console.log(json_1);
Then See in browser console what is your object and if the JSON converting your object properly.
If that is ok , Your request should be done currectly. And try to see what are the data you getting as response with:
success: function (data) {
consoel.log('response below');
console.log(data);
}
You will find the error. I hope.