Closure CavesISSUE #22 of 61

array methods · find · findIndex · some · every

LambdaVSThe Mutator

Lambda saysfind, findIndex, some, and every search and test arrays.

find returns the first matching item (findIndex its index); both return undefined/-1 if none match. some returns true if any item passes; every if all do. They short-circuit — stopping as soon as the answer is known — which makes them efficient.

Power-ups you unlock

find → first match · findIndex → its index
some → any match? · every → all match?
find returns undefined / findIndex returns -1
They short-circuit for efficiency

The Mutator attacks — common mistakes

Using filter()[0] instead of find
Confusing some (any) with every (all)
Expecting find to return all matches

Boss battleFind the first user over 18, then check if every user is active.

Example code

<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre id="o"></pre>
<script>const ages=[12,17,21,30]; const first=ages.find(a=>a>=18); const allAdult=ages.every(a=>a>=18);
document.getElementById('o').textContent='first adult='+first+' allAdult='+allAdult;</script></body></html>

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