Dynamic Javascript condition in For loop

Question

Please review the code below, note the condition of my for loop depends on the step parameter.

Rather than every time the condition is executed it determines which branch to use, I would like to test that once - I had supposed I could create a delegate or of the condition but it doesn't seem to work.

Is it possible in JS to do this?

Code:

function(start, end, step) {
 if (step === undefined) {
 step = 1;
 }
 var result = [];
 for (; (step < 0) ? start >= end : start <= end; start += step) {
 result.push(start);
 }
 return result;
}

My attempt:

function(start, end, step) {
 if (step === undefined) {
 step = 1;
 }
 var condition = (step < 0) ? start >= end : start <= end;
 var result = [];
 for (; condition; start += step) {
 result.push(start);
 }
 return result;
}

• Carcigenicate: That won't work since the condition is evaluated before start is ever changed. A hack way would be to define each as a function instead. There's definitely a better way though. I'll walk on it.

Answer 1

To do this, you need to make condition a function, like below. But even if you do, the condition is still executed at every iteration of the loop.

 var condition = (step < 0) ?
 function(start){
 return start >= end;
 } :
 function(start){
 return start <= end;
 };
 var result = [];
 for (; condition(start); start += step) {
 result.push(start);
 }