array.push不是函数 - 使用reduce时

Question

有人可以帮我理解这里发生的事情吗？

let firstArray = [];
firstArray.push(1);
firstArray.push(1);
firstArray.push(1);
console.log("firstArray", firstArray); // result [ 1, 1, 1 ] - as expected.



let secondArray = [1, 2, 3].reduce((acc, item) => {

    console.log("acc", acc);
    console.log("typeof acc", typeof acc);

    // on first passing, the accumulator (acc) is Array[] == object.
    // on the second passing the acc == number.

    // but why?
    /// i expect to get [1,1,1] as my secondArray.
    return acc.push(1);

}, []);

console.log("secondArray", secondArray); 

程序崩溃"acc.push不是一个函数"

并检查accumulator我们有push方法的第一个记录的节目 - 这是一个真正的功能:

Answer 1

返回值Array#push是推送后数组的新长度.这意味着在第二次迭代中acc是一个数字,它没有push方法.

修复很简单 - 将push和return语句分开:

const secondArray = [1, 2, 3].reduce((acc, item) => {
    acc.push(1);

    return acc;
}, []);

console.log(secondArray);