Angular2 - Keyup require a clarification

In my app, conditionally i am adding a class. and when the user enter something i am checking the value and accordingly i am adding the class name. it works fine.

but it only updates on set of (keyup)='0' - setting some value on keyup. this is not like angular 1 here.

so any one explain me why do we set the (keyup)=0 here? and what it do for us?

here is my code :

import {Component} from "angular2/core"

@Component({

    selector : 'my-component',

    template : `
                <h2>My Name is: {{name}} 
                    <span [class.is-awesome]="formReplay.value === 'yes' ">So good</span>
                </h2>
                <input type="text" #formReplay (keyup)="0" />
                `,

    styles  : [`

        .is-awesome{
            color:green;
        }

    `]

})

export class MyComponent { 
    name = "My Name";   
}