const arr = [1,4,9]
const newArr = arr.map(item => {
return item + this.a
},{a:1})
console.log(newArr) // [NaN, NaN, NaN]
const arr = [1,4,9]
const newArr = arr.map(item => {
return item + this.a
},{a:1})
console.log(newArr) // [NaN, NaN, NaN]