reactJs中的.map()没有返回任何内容

const array = [1, 2, 3];
const newArray = array.map(item => item * 2);
console.log(newArray); // [2, 4, 6]

const emptyArray = [];
const newArray = emptyArray.map(item => item * 2);
console.log(newArray); // []

const array = [1, 2, 3];
const newArray = array.map(item => {
  // 没有返回值
});
console.log(newArray); // [undefined, undefined, undefined]