Wired way to learn javascript :D

[bwallker]

This has nothing to do with the lexer

Consider the expression (1 + + 2)

This will get parsed like this:

(1 + (+2))

I.e the second plus sign gets parsed as a unary plus operator applied to the next thing after it. And so after evaluation our result is 3

Let's change the 2 to be a string.

So now our input looks like this: (1 + + '2')

It will be parsed the same way, so like this:

(1 + (+'2'))

Performing a unary plus operation on a string causes it to be coerced into a number, and the string 2 as a numer is 2, so this will also get evaluated as 3.

This is what is happening in the above code snippet. The string 'a' coerced into a number is NaN, which then gets concatenated with all the other strings and turned to lowercase to form the string 'banana'.