How can I do: var value = foo(bar); Where foo a function that looks up the value through a JSON request

Question

Coming from a PHP background I run into this kind of problem often when I'm programming with JavaScript & jQuery. I need a function that needs to take a variable and do a server lookup to get a status result back.

Rather than having to repeat the same code (which I am doing now and my boss dislikes) in 4 different places, I would prefer it to be a function I can call from anywhere.

The actual code is a lot more complex, I stripped it down to the basic concept for the purposes of this question.

I tried using "async: false" so that the function would wait for the ajax call to complete before returning, but it didn't work.

The solution likely is to use a Callback function. How exactly does this work and how would I need to structure my code to achieve this universally in different locations of my app (code)?

var sample = "ABC12345";
var samplestatus = getStatus(sample);
console.log("!!!!" + samplestatus + "!!!!");        

function getStatus(samplenumber) {  
    var jsonurl =  "lookup.php?s="+samplenumber;
    $.ajax({
        url: jsonurl,
        dataType: 'json',
        async: false,
        success: function(data1) {
            var s_status;
            if (typeof(data1[0]) !== 'undefined') {
                var data = data1[0];
                s_status = data.STATUS;
                console.log("Sample " + samplenumber + " has a status of "+s_status);
                return(s_status);
            } else {
                return(0);  
            }
        }
    });     
}

The output:

Sample ABC12345 has a status of COMPLETED
!!!!undefined!!!!

Answer 1

You should return from the function you call.

function getStatus(samplenumber) {
    var jsonurl  ="lookup.php?s="+samplenumber;

    return $.ajax({
        url: jsonurl,
        dataType: 'json',
        async: false,
        success: function(data1) {
            var s_status;
            if (typeof(data1[0]) !== 'undefined') {
                var data = data1[0];
                s_status = data.STATUS;
                console.log("Sample " + samplenumber + " has a status of "+s_status);
                return s_status;
            } else {
                return 0;  
            }
        }
    });
}