This functions helps to verify if a CPF (brazilian document) is valid.

cpf.js

function verify_cpf(cpf){
    /* This functions helps to verify if a CPF (brazilian document) 
    it's valid. Returns true if it is, false otherwise */
    cpf = cpf.replace(/\./g, "").replace(/\-/g, "");
    if (cpf.length != 11){
        return false;
    }

    var tt = 0, d =0;
    for (var t=9; t>=9 && t<11; t++){
        d = 0;
        for (var c=0; c<t; c++){
            d += parseInt(cpf.substring(c, c+1)) * (t + 1 - c);
            tt = c;
        }
        d = ((10 * d) % 11) % 10;
        
        if (parseInt(cpf.substring(tt+1, tt+2)) != d){
            return false;
        }
    }
    return true;
}