JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = [
  {
    "year": "2011",
    "activity": "bowling"
  },
  {
    "year": "2009",
    "activity": "shopping",
  },
  {
    "year": "2011",
    "activity": "cooking"
  },
  {
    "year": "2006",
    "activity": "singing"
  }
]

var arr = arr.reduce((unique, o) => {
  if(!unique.some(obj => obj.year === o.year)) {
    unique.push(o);
  }
  return unique;
},[]);


console.log(arr);