['1', '2', '3']. Map (parseInt) What
this output is a very remote knowledge point, it will cause you to be surprised every time you read it, but after reading it, it is very simple , After a while, I forgot to get rid of everything, so I decided to write a blog to remind myself:
output: [1, NaN, NaN].
First let us review, the first parameter callback of the map function:
then parseInt function
The parameters received by these two functions are shown above.
After understanding these two functions, we can simulate the operation
parseInt ('1', 0) // When radix is 0, and the string parameter does not start with "0x" and "0", the base 10 is used. At this time, return 1
parseInt ('2', 1) // In the number represented by 1 (1 base), the maximum value is less than 2, so it cannot be parsed, and return NaN
parseInt ('3', 2) // The base is Among the numbers represented by 2 (binary), the maximum value is less than 3, so it cannot be parsed. The NaN
map function returns an array, so the final result is [1, NaN, NaN]
This is the explanation of these two functions by MDN and W3School.
