1.方法一

let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice'];
let namesNum = names.reduce((pre,cur)=>{
// (cur in pre)  判断对象中是否包含某个key属性
 	if(cur in pre){
		pre[cur] ++ ;
	}else {
		pre[cur] = 1;
	}
	return pre;
},{});
console.log(namesNum)   //  {Alice: 2, Bob: 1, Tiff: 1, Bruce: 1}