jquery - 如何让函数等待jquery ajax完成

Question

我有一个登录表单，当用户单击提交按钮时，我有一个主函数，我调用它来决定页面是否应该迁移。在主函数中，我调用了另外两个函数:一个用于检查用户名和密码字段是否为空，第二个函数有一个ajax，用于检查用户名和密码的组合是否正确:问题是带有ajax的函数无法正常工作，因为 main 函数不等待带有 ajax 的内部函数完成(异步):这是示例代码:

<h3 id="myerror" style="display:none;">Invalid username or password</h3>

<form action="mylogin.php" onSubmit="return mymain()">
username<input type="text" id="myuname">
password:<input type="password" id="mypass">
</form>

//and the script

<script>

function mymain() {
    if (is_not_empty() && is_in_database()) {
        return true;
    } else {
        return false;
    }
}

function is_not_empty() {
    var uname = $("#myuname").val();
    var pass = $("#mypass").val();
    if (uname == "" && pass == "") {
        $("#myerror").css("display", "block");
        return false;
    } else {
        return true;
    }
}

var a;

function isthere() {

    var uname = $("#myuname").val();
    var pass = $("#mypass").val();

    //the ajax php below returns either isthere or notthere with reference to the username 
    and password combination.

    $.post("http://localhost/passtester/pass1.php", {
        username: uname,
        password: pass
    }, function (feedbak) {
        a = feedbak;
    });
    if (a == "isthere") return true;
    if (a == "notthere") return false;
}
</script>

我非常感谢您的帮助

Answer 1

您无法从异步方法返回值，而是需要使用回调方法，例如

function mymain() {
    if (is_not_empty()) {
        is_in_database(function (isthere) {
            if (isthere) {
                $('form').submit();
            }
        })
    }
    return false;
}

function is_not_empty() {
    var uname = $("#myuname").val();
    var pass = $("#mypass").val();
    if (uname == "" && pass == "") {
        $("#myerror").css("display", "block");
        return false;
    } else {
        return true;
    }
}

function is_in_database(callback) {

    var uname = $("#myuname").val();
    var pass = $("#mypass").val();

    //the ajax php below returns either isthere or notthere with reference to the username     and password combination.

    $.post("http://localhost/passtester/pass1.php", {
        username: uname,
        password: pass
    }, function (feedbak) {
        callback(feedbak == "isthere")
    });
}

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