Question

Possible Duplicate:
Question on this JavaScript Syntax (“What Does This Do?”)

in this article i found this:

/xyz/.test(function(){xyz;})

i looked at this and i coudn’t figure out how does the xyz passed to the invoker. so i did some similar test in the console:

/xyz/.test(function(){xya;}) > false
/xyz/.test(function(){xyz;}) > true    

/xyz/.test(function(){'xya';}) > false
/xyz/.test(function(){'xyz';}) > true

/xyz/.test(function(){console.log('xya');}) > false
/xyz/.test(function(){console.log('xyz');}) > true

/xyz/.test(function(xya){}) > false
/xyz/.test(function(xyz){}) > true

/fuc/.test(function(){}) > false
/func/.test(function(){}) > true

it seems that the .test() function converts the argument to string and then does the test. so why /xyz/.test(function(){xyz;}) used rather than /xyz/.test('xyz')?

Answer 1

Its effectively testing that:

(function(){xyz;}).toString()

returns recognizable javascript source code:

"(function(){xyz;})"

as opposed to something funky that some implementations may return.

It uses .test to convert the function to a string then verifies that an internal token (xyz) is visible in the result.