Question

When I run the following codes, the alert popup displays undefined. I thought it would return either true or false instead. Please can someone explain how the checkLoginStatus() function excutes. Thanks.

function checkLoginStatus() {
$.get("func.php", {op:'login_status', r:Math.random()}, function(data) {
    if (data == "Yes") {
        showSalesView();
        return true;
    } else {
        loginView();
        return false;
    }   
});

}

alert(checkLoginStatus());

Answer 1

There’s a couple things wrong.

One, you’re performing an asynchronous call within the function, so by the time the call has come back, checkLoginStatus has already returned. It essentially looks like this:

function checkLoginStatus() {
    $.get("func.php", {
        op: 'login_status',
        r: Math.random()
    }, function(data) {
        if (data == "Yes") {
            showSalesView();
            return true;
        } else {
            loginView();
            return false;
        }
    });
    // return undefined
}

Second, you’re returning within the callback of another function, so that return affects the return value of the callback to $.get

You want to use callbacks. So,

function checkLoginStatus(callback) {
    $.get("func.php", {
        op: 'login_status',
        r: Math.random()
    }, function(data) {
        if (data == "Yes") {
            showSalesView();
            callback(true);
        } else {
            loginView();
            callback(false);
        }
    });
}

and then

checkLoginStatus(function(result) {
    alert(result);
});