[DOCS] Make scrollbar API reference docs public

[willeastcott]

Fixes #1729.

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[ElsaMeng]

if(this.entity.scrollbar){
this.app.on('set:value',function(value){
this.updateValue(value);
});
}

[ElsaMeng]

hello, guys,I already make a scrollbar, but u see up there,when I grab the handle to change the value, it doesn't execute the function.I am confused.So how to use the event 'set:value'.Please help.Thanks a lot.

[willeastcott]

I think you mean to do:

if (this.entity.scrollbar) {
    this.entity.scrollbar.on('set:value', function (value) {
        this.updateValue(value);
    });
}

[ElsaMeng]

it works.Thanks again :)