What's wrong with this way of writing?

What's wrong with this way of writing? Why is it different from writing then (function (RS) {} when RS cannot be found??

let vm = new Vue({
            el: '#wrap',
            data: {
                rs: ''
            },
            methods: {
                getData(type, url, dataObject, okcallback, ercallback) {
                    if (String(type).toLowerCase() == 'get' && dataObject) {
                        axios.get(url, {
                            params: dataObject
                        }).then(okcallback)
                            .catch(ercallback)
                    } else if (!dataObject) {
                        axios.get(url).then(okcallback)
                            .catch(ercallback)
                    } else {
                        axios.post(url, qs.stringfy(dataObject)).then(okcallback).catch(ercallback)
                    }
                },
                resultSuccess(rs) {
                    console.log('aaa');
                    // vm.rs = rs;
                    // console.log(vm.rs, rs);
                },
                resultError(err) {

                }
            },
            mounted() {
                console.log('mounted over');
                this.getData('GET', url,'', this.resultSuccess, this.resultError);
            },
        })