set a variable inside ajax function - ajax

Question

Why does the usernameOK=1; statement in the ajax function not stay set when I use the alert statement after the $.post function? I need a way to use a variable as a condition for an if statement.
function validateRegistration() {
var username = document.getElementById("userName").value;
var fname = document.getElementById("fName").value;
var lname = document.getElementById("lName").value;
var email = document.getElementById("email").value;
var confirmEmail = document.getElementById("confirmEmail").value;
var password = document.getElementById("userpass").value;
var confirmPass = document.getElementById("confirmPassword").value;
var usernameOK = 0;
$.post("action.php", { field: 'doesUsernameExist', username: username },
function(result){ //if the result is 1
if(result == 1){ //show that the username is available
usernameSuc.innerHTML= username + " is Available.";
var usernameOK=1;
}else if(result == 0){ //show that the username is NOT available
usernameErr.innerHTML="User name: "+username+" is not
available.";
} else {
usernameErr.innerHTML="Something is Wrong";
}
});
alert("usernameOK: "+usernameOK); //This doesn't work. only prints a zero, never 1
if (usernameOK == 1) {
if ((username.length > 5) && (!(/[^a-zA-Z0-9_-]/.test(username)))){
if((fname != "") && (lname != "")){
if((email != "") && (email == confirmEmail)){
if (((email.indexOf(".") > 0) && (email.indexOf("#") > 0))
&& !/[^a-zA-Z0-9.#_-]/.test(email)){
if ((password.length > 7) && (/[a-z]/.test(password))
&& (/[A-Z]/.test(password)) && (/[0-9]/.test(password))){
if (password == confirmPass) {
document.getElementById("submit").className = "btn btn-success";
document.getElementById("submit").removeAttribute("disabled");
}
}
}
}
}
}
} else {
document.getElementById("submit").className = "btn btn-success disabled";
}
}

Answer 1

Figured out a solution. Thought I would post it in case it would help someone else. Changed the order and moved the ajax inside all the conditional if statements so it is the last thing to check instead of the first.
function validateRegistration() {
var username = document.getElementById("userName").value;
var fname = document.getElementById("fName").value;
var lname = document.getElementById("lName").value;
var email = document.getElementById("email").value;
var confirmEmail = document.getElementById("confirmEmail").value;
var password = document.getElementById("userpass").value;
var confirmPass = document.getElementById("confirmPassword").value;
if ((username.length > 5) && (!(/[^a-zA-Z0-9_-]/.test(username)))){
if((fname != "") && (lname != "")){
if((email != "") && (email == confirmEmail)){
if (((email.indexOf(".") > 0)
&& (email.indexOf("#") > 0))
&& !/[^a-zA-Z0-9.#_-]/.test(email)){
if ((password.length > 7)
&& (/[a-z]/.test(password))
&& (/[A-Z]/.test(password))
&& (/[0-9]/.test(password))){
if (password == confirmPass) {
$.ajax({
type: "POST",
url: "action.php",
data: {field: 'doesUsernameExist', username: username },
async: false,
success: function (result) {
if(result == 1) {
document.getElementById("submit").className = "btn btn-success";
document.getElementById("submit").removeAttribute("disabled");
} else {
document.getElementById("submit").className = "btn btn-success disabled";
document.getElementById("submit").setAttribute('disabled', true);
}
},
error: function (result) {
pass = "error"
alert("There was an error with the database");
}
});
}
}
}
}
}
} else {
document.getElementById("submit").className = "btn btn-success disabled";
document.getElementById("submit").setAttribute('disabled', true);
}
}