Use typescriptin vue, when overide one method in child component, in this method cannot call parent method?

[hesi726]

It only happened in Vue. (In typescript it works).

I use vue-cli to create a project and accord the
vuejs/vue-cli#1104
TypeStrong/fork-ts-checker-webpack-plugin#111
to split the .ts, .vue file in tow file.
and i write the follows code.

BaseComponent.ts

`import { Component, Prop, Vue } from 'vue-property-decorator';
@component({})
export default class BaseComponent extends Vue {
/**
* value changed
*/
public on_value_changed() {
this.before_value_changed();
}

/**
 * nothing to do but log one string
 */
public before_value_changed() {
    console.log('before_value_changed');
}

}
`
HelloWorld.ts

`import { Component, Prop, Vue } from 'vue-property-decorator';
import BaseComponent from '@/components/BaseComponent';

@component({})
export default class HelloWorld extends BaseComponent {
// @prop() private msg!: string;
private count: number = 12;

/**
 * override the before_value_changed function
 */
public before_value_changed() {        
    super.before_value_changed();  // **// will error**
    this.count++;
}

}
`
HelloWorld.vue

<template> <div class="hello"> <button @click='on_value_changed'>Test</button> {{count}} </div> </template>

when in the before_value_changed in HelloWorld.ts ， use super.before_value_changed call the before_value_changed method of BaseComponent， it will product error.

HelloWorld.ts?b79b:13 Uncaught TypeError: Cannot read property 'call' of undefined

in typescript, it work fine.
http://www.typescriptlang.org/play/index.html:

`class BaseComponent {
public before_value_changed() {
}
public on_value_changed() {
this.before_value_changed();
return "Hello, ";
}
}

class HelloWorld extends BaseComponent {
public before_value_changed() {
console.log('beforeGreet');
super.before_value_changed();
}
}
let hello = new HelloWorld();

let button = document.createElement('button');
button.textContent = "Say Hello";
button.onclick = function() {
alert(hello.on_value_changed());
}
document.body.appendChild(button);`

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