Transform forEach loops with if to forEach with a filter #190

aboyton opened this Issue Oct 11, 2016 · 2 comments


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aboyton commented Oct 11, 2016

It's a somewhat common pattern to have an if statement being the only thing in a forEach loop.

numbers.forEach(number => {
    if(number % 2 === 0) {

This could be transformed to something more functional with a filter.

numbers.filter(number => {
    return (number % 2 !== 0);
}).forEach(number => {

While this isn't a style everyone might like, I do think it's in the direction much ES6 code is heading and thus I think a useful transformation.

@nene nene added the enhancement label Oct 11, 2016
nene commented Oct 11, 2016 edited

Yep, this looks like a great idea.

Though in your code example, you have reversed the condition inside filter. A simple mistake I guess.

Would be nice to also have a transform from for-loop to, but it seems much trickier. With for-loop one often transforms the array in-place, relying on side-effects, while with .map() you'd be creating a new array... which can be difficult to map to equivalent code. There are some patterns though:

const result = [];
array.forEach(item => {
    result.push(item * 2);
// --->
const result = => item * 2);
aboyton commented Oct 11, 2016

Argh, even in such a simple example I still make a typo. Guess this is why I like lebab so much ;)

Definitely agree that we could do a lot more transformations like this. map would be a great one, as would reduce. I figured that I'd start by suggesting a simple example that I thought I'd know how to implement to test the waters with seeing what sorts of transformations that you are interested in doing with lebab.

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