How can I call a method from html attribute in vue js

I have a form and I need to call a method from a placeholder and also from other types of html attribute.

Is there anyways I can call a vue method? Here is what I am trying to do

<input type="text" class="form-control" v-model="user.userName" 
 placeholder=t("un") required> // want to call method t() from the placeholder

It seems this method cannot be called this way. Is there any other ways to achieve this?

And my method is

methods: {
   t(key){
        console.log(key)
        var local='fr';
        return this.trans(key,local);
      }
}