解决Django中在.js文件中用ajax请求后端,找不到CSRF问题

function getCookie(name) {
    var cookieValue = null;
    if (document.cookie && document.cookie !== '') {
        var cookies = document.cookie.split(';');
        for (var i = 0; i < cookies.length; i++) {
            var cookie = jQuery.trim(cookies[i]);
            // Does this cookie string begin with the name we want?
            if (cookie.substring(0, name.length + 1) === (name + '=')) {
                cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
                break;
            }
        }
    }
    return cookieValue;
}


var USERNAME = '';
$('document').ready(function(){


    $('#login_submit').click(function(){
        var csrftoken = getCookie('csrftoken');
        var username = $('#username').val();
        var password = $('#password').val();

        $.ajax({
            cache: false,
            type: "POST",
            url: "/signin/",
            dataType:'json',
            async: true,
            data:{
                username: username, //用户名
                password: password  //密码
            },
            success: function(data) {
                 if (data.status == 'fail') {
                        alert('用户名或密码错误')
                 }
                 if (data.status == 'fail1') {
                     alert('用户名必填并且密码必须要五位以上')
                 }
                 if(data.status == 'success') {
                     window.location.href = "/index";
                 }


            },
            beforeSend: function(xhr, settings) {
              xhr.setRequestHeader("X-CSRFToken", csrftoken);
            }
        });
    });