Question

this had me surprised:

var parts = email.split('@');
if (parts < 2) {

reference: https://github.com/Kicksend/mailcheck/blob/master/src/jquery.mailcheck.js#L21-22

essentially, it looks like:

var a = [null, null, null]
a < 2 // false

var b = [null]
b < 2 // true

so it seems like it works but I want to know why, what coercion actually happens for it to do this? as the intent here was to bail if less than 2 parts come from the email string, i would have expected it to always pass due to the array defined being truthy – it ought to create an array with at least 1 member even on an empty string.

i would always prefer to use array.length. is the above safe?

Answer 1

It’s a string and then number conversion that’s happening, since arrays can’t be directy compared with the < operator. First it will do a string comparison but with the number it will then do a number comparsion.

Note that:

• [null, null, null] == ",,"
• [null] == ""

And:

• +",," is NaN
• +"" === 0

Now it makes sense because 0 < 2 === true but NaN < 2 === false.

It’s therefore not a meaningful expression indeed. [null, null] < 3 is false because "," < 3 is essentially doing NaN < 3.