MediaWiki:Common.js

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/* Any JavaScript here will be loaded for all users on every page load. */

function getCookie(name) {
  match = document.cookie.match(new RegExp(name + '=([^;]+)'));
  if (match) return match[1];
}

var lang = getCookie('lang');

$.ajax({
    url: 'api.php',
    data: {
        action: 'query',
        meta: 'userinfo',
        uiprop: 'options',
        format: 'json'
    },
    xhrFields: {
        withCredentials: true
    },
    dataType: 'json'
}).done(function (data){
    var userid = data.query.userinfo.id;
    var currentLang = data.query.userinfo.options.language;

    if(username != 0 && lang && lang != currentLang){
        $.ajax({
            url: 'api.php',
            data: {
                action: 'query',
                meta: 'tokens',
                format: 'json'
            },
            xhrFields: {
                withCredentials: true
            },
            dataType: 'json'
        }).done(function (data){
            $.ajax({
                url: 'api.php',
                method: 'POST',
                data: {
                    action: 'options',
                    format: 'json',
                    token: data.query.tokens.csrftoken,
                    optionname: 'language',
                    optionvalue: lang
                },
                xhrFields: {
                    withCredentials: true
                },
                dataType: 'json'
            }).done(function (data){
                location.reload();
            });
        });
    }
});