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Conan
Conan

Posted on • Edited on

forEach / break / continue

#javascript #looping

Photo by Dan Meyers on Unsplash

A short Q&A on loops of the standard and functional variety, breaking out of them, and skipping iterations.

All code below assumes the following header:

const { log } = console const oneThousandItems = () => Array.from({ length: 1000 })
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So, the question is:

"At the end of each run, what will the value of index and count be?" 🤔

1. for vs. forEach, full-loops 

// 1a) function forLoop() { let index = 0 let count = 0 for (; index < 1000; index += 1) { count = count + 1 } log('index === ', index) log('count === ', count) } // 1b) function usingForEach() { let index let count = 0 oneThousandItems().forEach( (_, _index) => { index = _index count = count + 1 } ) log('index === ', index) log('count === ', count) }
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Next up, breaking-out of loops:

2. for vs. some vs. every, broken loops 

// 2a) function breakLoop() { let index = 0 let count = 0 for (; index < 1000; index += 1) { if (index > 499) { break } count = count + 1 } log('index === ', index) log('count === ', count) } // 2b) function usingSome() { let index let count = 0 oneThousandItems().some((_, _index) => { index = _index if (index > 499) { return true } count = count + 1 }) log('index === ', index) log('count === ', count) } // 2c) function usingEvery() { let index let count = 0 oneThousandItems().every((_, _index) => { index = _index count = count + 1 if (index < 499) { return true } }) log('index === ', index) log('count === ', count) }
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Finally, skipping to the next iteration:

3. for vs. forEach, skipped loops 

// 3a) function continuedLoop() { let index = 0 let count = 0 for (; index < 1000; index += 1) { if (index > 249) continue count = count + 1 } log('index === ', index) log('count === ', count) } // 3b) function usingForEach() { let index let count = 0 oneThousandItems().forEach( (_, _index) => { index = _index if (index > 249) return count = count + 1 } ) log('index === ', index) log('count === ', count) }
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If you need a little help, I made a corresponding interactive version of the article that offers some very basic visuals.

I'm not sure if they help intuit what's going on, but they give the answers at least! Did they meet your expectations?

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