ES6 Alternate While Loop

Question

I have the following code I've been developing, an alternate while loop:

_while = (cond, act) => cond && act() & _while(cond, act)

In this case act() is intended to alter the end result of cond with each iteration until cond is evaluated to false , to which then the loop is meant to end...

I've tried to test this out by attempting to determine the length of a string through stepping through the string using my code. As a result, my code is the following:

len = 0; _while(!!("qwerty")[len], ()=>++len);

Now, my thoughts were that this code will basically step through and test for the presence of each character within the string, incrementing len until it attempts "qwe"[6] which is undefined , and the !! renders the undefined returned value to false , exiting the loop, with the value of len being equal to 6 ...

However, I'm not even getting that far... for some reason this loop keeps going, and gives up with an error of InternalError: too much recursion

Can anyone see what I've done wrong with my code? I'd like to preserve what I can of my original code without having to resort to a native for or while loop...

Answer 1

The expression !!("qwerty")[len]) is evaluated before the call to _while is actually made. At that time, len is 0 , so the result of the expression will be true .

To fix this, you could require cond to be a function, much like act is. This way, you can evaluate the condition each time through the loop. I guess it would look like this (though I'm not JavaScript savvy):

_while = (cond, act) => cond() && act() & _while(cond, act)

The given example would then become

len = 0; _while(()=>!!("qwerty")[len], ()=>++len);