How to construct a JavaScript for loop with a function

Question

I'm constructing a loop for with a function.

The function loop takes a value, a test function, an update function, and a body function. Each iteration, it first runs the test function on the current loop value and stops if that returns false. Then it calls the body function, giving it the current value. Eventually, it calls the update function to create a new value and starts from the beginning.

loop(10, n => n > 0, n => n - 1, console.log);

function loop(a, b, c, d) {

    let currentValue = a;
    let i;
    for (i = 0; i < currentValue; i++) {
        if (b(currentValue)) {
            d(currentValue);
            update(c);

            function update(c) {
                var executeUpdate = c(currentValue);
                currentValue = executeUpdate;
            };
        } else {
            return;
        }
    };
}


// OUTPUT: 10, 9, 8, 7, 6

Why does this function stop at 6 instead of 1?

b returns a bool, and current value is in your example int. how does your if statement work? if (bool < int) — Fallenreaper
– Fallenreaper, Commented Jun 28, 2018 at 13:53
@Fallenreaper Right, I just edited the function. Oddly the output doesn't chance. — leonardofed
– leonardofed, Commented Jun 28, 2018 at 14:00

Isaac · Accepted Answer · 2018-06-28 14:02:05Z

1

function update(c) {
  var executeUpdate = c(currentValue);
  console.log('value of exeucteUpdate: ',executeUpdate, 'when i:', i)
  currentValue = executeUpdate;
};

Do a console.log at your update function, you will notice when i == 4, executeUpdate is 5 and you updated the value of forloop and hence the loop terminates at this particular loop

answered Jun 28, 2018 at 14:02

Isaac

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1 Comment

leonardofed Over a year ago

Gotcha. Anchoring the for loop check clause to a static value of a, (i = 0; i < a; i++) would fix this.

libik · Accepted Answer · 2018-06-28 13:58:21Z

1

You can use few console.logs to see it.

Actually the for-cycle ends when currentValue and i equals 5, therefore the condition is not met and cycle terminates.

However your condition does not make any sense, you are comparing true to some number (as you can see in the logs)

loop(10, n => n > 0, n => n - 1, console.log);

function loop(a, b, c, d) {

    let currentValue = a;
    let i;
    for (i = 0; i < currentValue; i++) {
        console.log(i, currentValue);
        console.log(b(currentValue), currentValue)
        if (b(currentValue) < currentValue) {
            d(currentValue);
            update(c);

            function update(c) {
                var executeUpdate = c(currentValue);
                currentValue = executeUpdate;
            };
        } else {
            console.log('I am not here');
            return;
        }
    }
    console.log('finished', i, currentValue);
}

answered Jun 28, 2018 at 13:58

libik

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1 Comment

leonardofed Over a year ago

True. I just edited the condition, but oddly the output it's still the same. > Actually the for-cycle ends when currentValue and i equals 5, therefore the condition is not met and cycle terminates. currentValue is set as 10.

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