Setter

components.my-component.js

import Ember from 'ember';
const { computed } = Ember;

export default Ember.Component.extend({
  theValue: computed({
    get() {
      return this._theValue;
    },
    
    set(key, newValue) {
      this._theValue = newValue;
      return this._theValue;
    }
  }),
  
  actions: {
    change() {
      this.set('theValue', 'goodbye');
    }
  }
});

templates.application.hbs

{{my-component theValue="hello"}}

templates.components.my-component.hbs

<p>The value is {{theValue}}</p>

<p><button {{action "change"}}>Change the value</button></p>

twiddle.json

{
  "version": "0.4.0",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.5/ember.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/1.13.5/ember-data.js"
  }
}