We need to create validators for each status. The validator will check if transition from current state is allowed or not.

Script
var validStatus = {
    'new': ['pending'],
    'pending': ['approved', 'rejected'],
    'approved': [],
    'rejected': []
}

var isValidStatus = function (currentStatus, newStatus) {
    return validStatus[currentStatus].indexOf(newStatus) >= 0;
};

isValidStatus('new', 'pending');