數組key值去重

const ary = [{
				a: 1,
				b: 12,
				c: 3
			}, {
				a: 1,
				b: 11,
				c: 111
			}, {
				a: 2,
				b: 18,
				c: 111
			}];
			const newArr = [];
			ary.map((item) => newArr.findIndex(({
				a
			}) => a === item.a) === -1 && newArr.push(item));
			console.log(newArr);

 有一個key值相同都不行：

var obj = {};
			arr = arr.reduce(function(item, next) {
				obj[next.key] ? '' : obj[next.key] = true && item.push(next);
				return item;
			}, []);
			console.log(arr); 

var result = [];
   var obj = {};
   for(var i =0; i<arr.length; i++){
      if(!obj[arr[i].key]){
         result.push(arr[i]);
         obj[arr[i].key] = true;
      }
   }