What Javascript type conversions are happening here?

I found a bug in a script that was written, and I'm having troubles figuring out exactly what is causing the issues. Specifically:

"49px" < 50 === false

There's two different conversions I can think of here:

49 < 50 === true
"49px" < "50" === true
"49" < 50 === true // just for the hell 开发者_如何学Goof it

I fixed it with:

parseInt("49px") < 50 === true

So why does this evaluate to false? What exactly is happening here?

If one operand is a number and another operand is a string, then the string is converted to a number and then the comparison is made.

If the string cannot be converted to a number, it gets converted to NaN, and the comparison always returns false.

When javascript is asked to compare a number with something else, it tries to convert that "something else" to a number. In this case, "49px" evaluates to NaN so NaN < 50 is false.