A more efficient way to run a function after a cycle is complete in Javascript

Question

Suppose I have the following Javascript code:

    var i = 0;

    var list = ['a','b','c'];

    for (var key in list) {
        
        // some other operations on list[key]

        // in case they are successful
        i = i + 1;
        
    }

    if (i == list.length) {
        console.log('cycle complete');
    }

The idea is that a certain function (in this case console.log) fires after the cycle is complete.

What would be a more efficient way to achieve the same tasks?

Maybe functional programming?

unclear what is supposed to be the check. Solutions would be dependent on what happens inside. — epascarello, Apr 09 '18 at 13:20
So, it only fires when all operations were successful? In this case, try `if (.every(...)) fn()` — georg, Apr 09 '18 at 13:46
[Don't use `for…in` enumerations on arrays!](https://stackoverflow.com/q/500504/1048572) Otherwise yes, that's fine. — Bergi, Apr 09 '18 at 14:55
I provided an answer but I decided to drop it, because this is an XY problem. In FP, you wouldn't implement that this way. — Matías Fidemraizer, Apr 12 '18 at 09:46

Lansana Camara · Accepted Answer · 2018-04-13T17:16:46.770

1

Assuming the operation in your for loop will evaluate to true or false, you could do something like this:

function countSucceeded(list: any[], iteratee: (key: string) => boolean): number {
    let count = 0;

    for (let i = 0; i < list.length; i++) {
        if (iteratee(list[i])) {
            count++;
        }
    }

    return count;
}

const list = ['foo', 'bar', 'baz'];
const test = (key: string): boolean => key.indexOf('foo') > -1;
const count = countSucceeded(list, test);

console.log(count); // 1

Now it is "functional", though you could get rid of the loop as well.

Update:

Here is how you could do the loop in a purely functional way:

function each(list, iteratee) {
    if (list.length == 0) {
            return;
    }

    iteratee(list.shift())

    return each(list, iteratee);
}

each([1, 2, 3], num => console.log(num)); // 1 2 3

edited Apr 13 '18 at 17:16

answered Apr 09 '18 at 13:45

Lansana Camara

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I see that your code snippet is TypeScript. OP is asking for a vanilla JavaScript solution... – Matías Fidemraizer Apr 12 '18 at 09:08
This was not meant to me a copy and paste solution. I used TypeScript for the readability, so he can easier see what was going on with my function arguments. – Lansana Camara Apr 12 '18 at 11:47
@Lansana thank you for your response! and how would I get rid of the loop completely? – Aerodynamika Apr 13 '18 at 15:32
@DmitryParanyushkin Update answer. Using divide and conquer with recursion to loop in a purely functional way. – Lansana Camara Apr 13 '18 at 17:17

A more efficient way to run a function after a cycle is complete in Javascript

1 Answers1