Why does parseInt yield NaN with Array#map?

Question

From the Mozilla Developer Network:

[1,4,9].map(Math.sqrt)

will yield:

[1,2,3]

Why then does this:

<

Answer 1

I'm going to wager that it's something funky going on with the parseInt's 2nd parameter, the radix. Why it is breaking with the use of Array.map and not when you call it directly, I do not know.

//  Works fine
parseInt( 4 );
parseInt( 9 );

//  Breaks!  Why?
[1,4,9].map( parseInt );

//  Fixes the problem
[1,4,9].map( function( num ){ return parseInt( num, 10 ) } );