vue props传值失败 输出undefined的解决方法

<code class="language-html"><div id="app"> 
<test :type="type"></test> 
</div> 
Vue.component("test", { 
  props: ['type'], 
  template: '<div @click="a">我是按钮{{type}}</div>', 
  methods: { 
   a() { 
    console.log(this.type); 
   } 
  } 
 }); 
var app = new Vue({ 
 el: '#app', 
 data: { 
 type: 'test' 
 } 
});</code> 

<div id="app">
<test :selectName="selectName"></test>
</div>
Vue.component("test", {
  props: ['selectName'],
  template: '<div @click="a">我是按钮{{selectName}}</div>',
  methods: {
   a() {
    console.log(this.selectName);
   }
  }
 });
var app = new Vue({
 el: '#app',
 data: {
 selectName: 'test'
 }
});

<div id="app">
<test :select-Name="selectName"></test>
</div>
Vue.component("test", {
  props: ['selectName'],
  template: '<div @click="a">我是按钮{{selectName}}</div>',
  methods: {
   a() {
    console.log(this.selectName);
   }
  }
 });
var app = new Vue({
 el: '#app',
 data: {
 selectName: 'test'
 }
});

this.$emit("selectchange","data");

this.$emit("selectChange","data");

this.$emit("select-change","data");