I am creating an array of pills and would like to add a data-* attribute to each item. But unfortunately I get a syntax error.

I tried changing the field name 'data-id' to 'dataId' but still wasn't able to query the field using `event.target.dataset.dataId`.

What is the right syntax for this? 


[Playground][1]


    import { LightningElement, track } from 'lwc';
    
    export default class App extends LightningElement {
    
        @track items = [
    
        ];
        handleClick(event){
            let obj ={
                label: 'test', 
                data-Id: 'my data id' <---- This is where I get syntax error
            }           
            this.items.splice(this.items.length,0,obj)  //adding new items to array
        }  
        copyPillToForm(event){
            console.dir(event.target.dataset.data-Id)
    
        }
    }


  [1]: https://developer.salesforce.com/docs/component-library/tools/playground/AOsUnbTGM/28/edit