Javascript is not totally sane:

  '\t\r\n' == 0 --> true

And not transitive:

  "false" == "0" --> false
  "0" == 0 --> true
  0 == false --> true
  false == "false" --> false

It's basically impossible to make a loosely typed equality perfect.

PHP is much more strict about the rules used when doing the comparison, javascript is more loose. It tries to guess.

When comparing a string to a number, if the string looks like a number it's converted to one. But if it doesn't, then instead the number get converted to a string.

This works well most of the time - but not always, since it can surprise you. PHP is more strict, so it doesn't work as often, but it fails more consistently, so it's easier to find the problem.

Another example:

  "1" == "01" --> false
  "01" == 1 --> true
  1 == "1" --> true