[Vuejs]-How to implement vue package

Replace to this (added var self = this;):

formSubmit: function(){
    console.log('form submit');

    var self = this;        

    axios({
        method: this.method,
        url : this.route,
        data : this.form
    }).then(function (response) {
        console.log(response);
        self.$toastr.s("ssss");
        //this.VueToastr.s("ssss");
    }).catch(function (error) {
        console.log(error);
    });
}

Upd.

Also, you can use arrow function as callback like this:

formSubmit: function(){
    console.log('form submit');
    axios({
        method: this.method,
        url : this.route,
        data : this.form
    }).then((response) => {
        console.log(response);
        this.$toastr.s("ssss");
        //this.VueToastr.s("ssss");
    }).catch(function (error) {
        console.log(error);
    });
}