小于和大于10

Question

I'm working on a random code challenge, and I cannot figure out for the life of me how this would be possible

function(obj) {
   if ( (obj < 10) && (obj > 10) ) {
     return true;
   }
}

Things I've tried are setting an interval to change the variable at 0ms(which ends up being browser default), making obj an life function that increments a global variable every time it's used, and a whole bunch of other seemingly less useful approaches. Any ideas here, or pointers for something obvious I'm missing?

Answer 1

The clue is in the variable name "obj". When objects are compared, their valueOf() method is called. If we supply a valueOf method that returns a different value every time:

 function test(obj) { if ( (obj < 10) && (obj > 10) ) { return true; } } var Obj = function() { var flag = false; this.valueOf = function() { if( flag ) { return 11; } flag = true; return 9; } } console.log( test( new Obj() ) ); 

The above object's toValue returns 9 the first time it's called (9 < 10) and 11 from then on (11 > 10).