title: Vue JS: this.$on event doesn't contain passed parameters
body: <p>Here are my components. I've successfully emitted parameters from the child component to the parent, but not from the parent to the child. The <code>console.log('In initDetail()');</code> line fires, which means the <code>$on</code> event is triggered, but <code>param</code> is undefined. I'm wondering why.</p>
  
  <p>Parent component:</p>
  
  <pre><code>components: {
    "child-component": ChildComponent
  }
  methods: {
    loadDetail() {
      this.$emit('loadDetailEvent', 'test');
    }
  }
  </code></pre>
  
  <p>Child Component:</p>
  
  <pre><code>mounted() {
    this.$on('loadDetailEvent', this.initDetail(param)); 
  }
  methods: {
    initDetail(param) {
      console.log('In initDetail()');
      console.log(param);
    }
  }
  </code></pre>
  
  <p>I've also tried calling a function right away. Neither the <code>console.log('$on event');</code> nor the <code>console.log(param);</code> lines print.</p>
  
  <pre><code>this.$on('loadDetailEvent', function(param){
    console.log('$on event');
    console.log(param);
  });
  </code></pre>