Use JavaScript for loops if you need to break out early
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The usefulness of the humble for
loop in modern JavaScript is rarely talked about. Apart from it being particularly useful in asynchronous operation scenarios, it can also make your code a lot more performant shall you need to break out of a loop early. Consider the following example:
const smallArray = [0, 2]; const largeArray = Array.from({ length: 1000 }, (_, i) => i); const areEqual = (a, b) => { let result = true; a.forEach((x, i) => { if (!result) return; if (b[i] === undefined || x !== b[i]) result = false; }); return result; } areEqual(largeArray, smallArray); // false // Will loop over all items in `largeArray`
Obviously, the code isn't optimized, but it highlights the issue of array methods, such as Array.prototype.forEach()
being unable to break out of the loop early. To counteract this, we could use a for
loop and an early return
instead:
const smallArray = [0, 2]; const largeArray = Array.from({ length: 1000 }, (_, i) => i); const areEqual = (a, b) => { for (let i in a) { if (b[i] === undefined || a[i] !== b[i]) return false; } return true; } areEqual(largeArray, smallArray); // false // Will only loop until the first mismatch is encountered