[Nightmare]

сделал так:

var checkFormulaName = function() {
    var returned;
    this.getFormula = function(name) {
        return $.ajax({
            url: '/formula/msp/check',
            type: 'POST',
            data: 'name='+name,
            dataType: 'json',
            async: false
        }).responseText
    }
}