How to load combo in a form from an external json server

version 9, I can not find how to do this, I look at the doc and ask chat gpt I can not get it to work.
I need a good example please

The code could be like below:

// myform.mycombo
// myjson: [ {myid:xxx, mycontent:xxx},...]
ajax.get(url,{para:para}).then(res=>{
    myform.getItem("mycombo").getWidget().data.parse(
        res.myjson.map(item=>{
            id:item.myid,
            value:item.mycontent,
        });  // end forEach
    ); // end parse
    myform.getItem("mycombo").getWidget.paint();
}).catch(err=>{
  console.log(err);
}); // end

thanks for your reply I will check out your code.
In the meantime, I found that
const testmethodDataSet = new dhx.DataCollection();
testmethodDataSet.load(
“http://get_testmethods.php”
);
works