Ajax post request front-end csrf token
You can take a look at the guide Enabling CSRF Protection 

&lt;script type="text/javascript"&gt;
    window.csrfTokenName = "{{ craft.app.config.general.csrfTokenName|e('js') }}";
    window.csrfTokenValue = "{{ craft.app.request.csrfToken|e('js') }}";
&lt;/script&gt;


var data = {
    // ...
};

// Add the CSRF Token
data[csrfTokenName] = csrfTokenValue;

$.post('/some/url', data, function(response, textStatus, jqXHR) {
    // ...
});