[jQuery] How can I return some value in jquery's callback function?

[jQuery] How can I return some value in jquery's callback function?


it didn't work when I 'return true' or 'return false', is there some
way to get it?
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var url='http://localhost/coudou/check/register.php?email=' + str;
    $.getJSON(url, function(res){
        if(res.registed){
            return true; // not work
        }else{
            return false; // not work
        }
    });