Why ['1', '5', '11'].map(parseInt) returns [1, NaN, 3] in Javascript

This code:

['1', '5', '11'].map(parseInt);

returns this:

[ 1, NaN, 3 ]

Run '['1', '5', '11'].map(parseInt)' in JavaScript console.

This behavior is because map callback function actually takes 3 arguments:

Screenshot of map() documentation

So you're actually calling parseInt with 3 args (parseInt take 2 arguments max).

The good way is be explicit:

['1', '5', '11'].map((n) => parseInt(n));