Create a truth table enumerating all possible parameter combinations for a function taking booleans. Arguments: target function, number of boolean arguments, string for true, string for false.

truthtable.js

function truthTable(fun, bits, t, f){
  var vars = bits || 4
	  , max = 1 << vars
	  , tStr = t || ' T '
	  , fStr = f || ' F '
	  , i, j, str, arr, set, res;
	for (i = 0; i < max; i++) {
		str = '';
		arr = [];
		for (j = vars - 1; j >= 0; j--) {
			set = ((i & (1 << j)) != 0);
			arr.push(set);
			str += set ? tStr : fStr;
		}
		res = fun.apply(null, arr);
		console.log(str + ' => ' + (res ? tStr : fStr) + ' [' + i + ']');
	}
}

This is a short one-line form (e.g. for pasting in node):
var tt = function(fun,bits,t,f){var vars=bits||4,max=1<<vars,tStr=t||' T ',fStr=f||' F ',i,j,str,arr,set,res;for(i=0;i<max;i++){str='';arr=[];for(j=vars-1;j>=0;j--){set=((i&(1<<j))!=0);arr.push(set);str+=set?tStr:fStr}res=fun.apply(null,arr);console.log(str+' => '+(res?tStr:fStr)+' ['+i+']')}};