每个ajax / jQuery.post（）结果返回前缀为变量'f'

Every jQuery.post() call returns the string prefixed with an unwanted letter 'f'.

function show_leads_zone_list(sel_value) {
$.post('<?php  echo base_url();?>lead_management/show_all_zone', {operation_id:sel_value}, function(data) {
    alert(data);
    $("#leads_zone_div").html(data);
    }); 
}

function in Controller:

function show_all_zone()
{

    echo "test";
}

on calling this function show_leads_zone_list() , it alerts "ftest". This happens with every ajax function.

You must have printed some variable which result the letter 'f' or may be printed the letter 'f' directly. If you are getting this letter in AJAX, make sure whether the same letter displaying on all pages or not. If so, view the source code and that will help you to find the location of this letter. Share your page link, if you have, to check the issue.