How to call cc.Component.EventHandler in custom component?

Cocos Creator
1

For example, I have a SubComponent:

cc.Class({
    extends: cc.Component,
 
    properties: {
        myCallback:{
            type:cc.Component.EventHandler,
            default:null
        }
    },
 
    onLoad(){
        this.scheduleOnce(function(){
            this.myCallback();
        }.bind(this),3);
    }
});

it would trigger myCallback after 3 seconds, the callback in Canvas:

cc.Class({
    extends: cc.Component,

    properties: {
    },
  
    test(){
        alert("test callback");
    }
});

Which already set the function at the UI:

p1
p11612×620 141 KB

but when running it, some errors:

TypeError: this.myCallback is not a function. (In ‘this.myCallback()’, ‘this.myCallback’ is an instance of cc_ClickEvent)

What is the reason?