Why does the map() method return the length of an array?

Question

JavaScript

Why is the map() method returning the length of the array in this code? Logically, after all, the object should be pushed

const arr = [
    {testKey: 'test-value'},
    {testKey1: 'test-value1'},
    {testKey2: 'test-value2'},
    {testKey3: 'test-value3'},  
]

let newArr = arr.map((keyValue)=>{
    return keyValue
}).push({newTestKey: 'new-test-value'})

console.log(newArr) // возвращает 5

i know it will work if i write
let newArr = arr.map((keyValue)=>{
return keyValue
})
newArr.push({newTestKey: 'new-test-value'})
console.log(newArr)

Answer 1

push

Return value
The new length property of the object upon which the method was called.