Wat (destroyallsoftware.com)

Fun fact: the creator of Javascript posts on HN. Maybe he'll answer your question.

   a = a

The JavaScript stuff, I think, comes from operator overloading. The plus operator is overloaded to allow adding strings to concatenate them, and it will do type conversion to get compatible types, so "wat"+1 results in the 1 being converted to a string, and then the strings are concatenated. Since the minus operator is not so overloaded, "wat"-1 instead is treated as numerical subtraction. JavaScript allows string to be used as numbers, so "123"-1 gives 122. However "wat" is not a string that represents a number, so gives NaN when forced to be treated as a number, and "wat"-1 is thus NaN.

JavaScript went down the path of being a "forgiving" language because it was intended to provide "extra" (non-core) functionality, under a lot of environments, in the hands of non-experts. It made sense at the time that it should fail silently rather than noisily to not crash the page it was on. It also tried to help amateurs who just banged on code until it did what they wanted, by generally doing something rather than nothing, and by trying to infer intended behavior from undisciplined code. It was never intended to make large-scale or robust applications, so it didn't make decisions that would facilitate that use-case.

http://trac.webkit.org/wiki/JSC

/System/Library/Frameworks/JavaScriptCore.framework/Versions/A/Resources/jsc

You can just do:

sudo ln /System/Library/Frameworks/JavaScriptCore.framework/Versions/A/Resources/jsc /bin/jsc

To be able to invoke it directly from the command line.

  $ php -r '::'
  Parse error: parse error in Command line code on line 1

Edit:

Hrm, if I try it on my DreamHost account, I get something more similar to yours:

  $ php -r '::'
  Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in Command line code on line 1

Also, I'm on an old version of node, but my output matches jsc.

  d8> ([] + [])
  
  d8> ([] + {})
  [object Object]
  d8> ({} + [])
  [object Object]
  d8> ({} + {})
  [object Object][object Object]

But maybe it is just because I write code for a living...

The first thing it should do is TypeError that null is not a string. Or don't join null fields because there is nothing there.

If is does convert null to '', then it should TypeError on string - int. If it is not going to TypeError it should do something sensible, like slice the string

  > Array(16).join("wat".slice(0,-1)) + " Batman!"
  'wawawawawawawawawawawawawawawa Batman!'

JavaScript nuttiness:

Now it's zero:

  > null + 1
  1

  > null + "text"
  'nulltext'

  > [null, null, null].join()
  ',,'

If it doesn't work, error:

  >>> "wat" - 1
  Traceback (most recent call last):
	  File "<stdin>", line 1, in <module>
  TypeError: unsupported operand type(s) for -: 'str' and 'int'

  >>> ','.join([None, None, None])
  Traceback (most recent call last):
	  File "<stdin>", line 1, in <module>
  TypeError: sequence item 0: expected string, NoneType found

  >>> ','.join([str(i) for i in [None, None, None]])
  'None,None,None'

  >>> ','.join([str(i) for i in [None, None, None] if i])
  ''

    function pad(n, c) { return Array(n+1).join(c); }

    // pad(6, "-") === "------"