[‘1’, ‘2’, ‘3’].map(parseInt)
> Array(3) [ 1, NaN, NaN ]  // why!!!
[‘1’, ‘2’, ‘3’].map(a => parseInt(a))
> Array(3) [ 1, 2, 3 ]

WHY !!!!!!!!!!!!!!

It’s stupid but a thing

- The second param of parseInt is radix
- The second param of map callback is index
=> so index is screwing it

++> parseInt is executed this way
Parseint(num, index, array) completely screwed

Simply put we can’t use directly parseInt.

Use the arrow function notation num => parseInt(num) and it’s more explicit. Better then making a function parseInt10() for that.

A good lesson: always care about all the parameters