I believe you know ajax function whichever in server and on client, whatever programing languages.
Therefore I just show you a sample code first.

Case study:
table name: ftest
require columns: ftest_jt_id, ftest_name, ftest_age, ftest_ave
api name: ‘js10’
IN: {“apino”:”js10″,”subquery”:”[‘age’:{age}]”}
OUT: {“result”:true or false, “Jetelina”:”[{“ftest_jt_id”:”{ftest_jt_id}”,”ftest_name”:”{ftest_name}”,”ftest_age”:”{ftest_age}”,”ftest_ave”:”{ftest_ave}”,”message from Jetelina”:””…..””}
execution sql: select ftest.ftest_jt_id,ftest.ftest_name,ftest.ftest_age,ftest.ftest_ave from ftest as ftest where ftest.ftest_age < {age};

hum, looks like a little bit strange in Json, but do not care, I work correctly.

const getAjaxData = (s) => {
        let pd = {};

        pd["apino"] = "js10";
        pd["subquery"] = "['age':30]";

        let dd = JSON.stringify(pd);
        let url = "http://localhost:8000/apiactions"
        $.ajax( {
            url: url,
            type: "post",
            data: dd,
            contentType: 'application/json',
            dataType: "json",
        }).done(function(result, textStatus, jqXHR) {
        }).fail( function( result ){
        }).always(function(result){
        });
    }

You know ‘apiactions’ is the callable webapi name, you throw your Json form of api forward to this webapi.
Indeed, this webapi has alternative name; ‘plzjetelina’ and ‘executionapi’, work as same as ‘apiactions’.