How Reduce function really work in JavaScript?

May 25, 2022

I’m trying to use reduce function in order to find the max length array in arrays
so I tried this approach at first but it didn’t work

const arrays = [[1],[3,3,4],[3,4],[4,5],[6]]
let maxLength = arrays.reduce( (acc, cur) => {
    return acc.length > cur.length ? acc.length : cur.length
})

console.log(maxLength) // output : 1

so I tried to get the length in another way and it worked

const arrays = [[1],[3,3,4],[3,4],[4,5],[6]]
let maxLength = arrays.reduce( (acc, cur) => {
    return acc.length > cur.length ? acc : cur
}).length

console.log(maxLength) // output : 3

Can someone Explain what is the difference between the two approaches ?

>Solution :

In the first code, the reduce function is returning a number, while in the second, it is returning an array. When you’re returning a number, the next time your function is called, it takes the length of a number, not an array. The second code is correct, because you’re taking the length of an array every time.