Question

var doCheck = function() {
    var data;

    $.ajax({
        url: 'check.php',
        data: 'ch=check',
        success: function(resp) {
            data = resp;
        }
    });
console.log(data);
    return data == 1;
};

The above code, regardless of the data only ever returns a 0 or a 1. Within the scope of the success callback, this is true. The argument resp has a value of 0 or 1 depending on input.

However, whenever I try to access a private variable (should not be affected by scope), nothing happens; and when console.log(data); is called all that is written to the console is undefined.

This function has no parent, so don’t worry about some other kind of scope interference.

Answer 1

Ajax is asynchronous. Which is why you have to organize your logic with callbacks:

var doCheck = function(callback) {
    var data;

    $.ajax({
        url: 'check.php',
        data: 'ch=check',
        success: function(resp) {
            callback(data == 1);
        }
    });
};

doCheck(function(result) {
    // result is true or false
});