Home Problem with a function taken as a function parameter that takes AJAX as its own parameter

Questions

Problem with a function taken as a function parameter that takes AJAX as its own parameter

November 11, 2021

I can console.log(arg) but not arg.response. Curious what is the reason behind // edit: when I console log arg I can clearly see response property with data

   function doAjax(param, lambda) {
        let _xhttp = new XMLHttpRequest();
        _xhttp.open("GET", param, true);
        _xhttp.send();
        _xhttp.onload = lambda(_xhttp);
    }
    
    doAjax("ALL_FRAMES", function(arg) {
         console.log(arg.response); --> prints blank field in console
         //allFrames = JSON.parse(arg.response);
    });

>Solution :

_xhttp.onload = lambda(_xhttp);

This means "call lambda(_xhttp) immediately, and then assign its return value to _xhttp.onload". You instead want to assign a function to onload, and that function will call lambda later on:

_xhtttp.onload = () => lambda(_xhttp);

// edit: when I console log arg I can clearly see response property with data

That is just a quirk of the way the dev tools handle logging objects. When logging an object, the object is not evaluated until you click on the object in your dev tools. So at the time the console.log ran it didn’t have the response yet, but by the time you click, it does have it.