结论：写了{}里面的要return，没写{}不加return

let arr = [
            {
                id: 1,
                name: 'aa',
                desc: 'aaaa'
            },
            {
                id: 2,
                name: 'bb'
            },
            {
                id: 3,
                name: 'aa'
            }
        ]
        let arr1 = arr.filter(item => item.name == 'aa')//正确
        // let arr2 = arr.filter(item =>  return item.name == 'aa' )  //报错
        let arr3 = arr.filter(item => {item.name == 'aa'})//为空
        let arr4 = arr.filter(item => { return item.name == 'aa' })//正确
        console.log(arr1, 'arr1') 
        // console.log(arr2, 'arr2');
        console.log(arr3, 'arr3');
        console.log(arr4, 'arr4');

arr1,arr4能正确输出，arr3没有取到正确的值是空的，arr2报错

原文转载于https://www.cnblogs.com/zcbj588/p/14699411.html