Closure CavesISSUE #60 of 61

ES2023 · array find from last · symbol.dispose

LambdaVSThe Mutator

Lambda saysES2023 added immutable array methods (toSorted, toReversed) and findLast.

New non-mutating array methods return a copy instead of changing the original: toSorted, toReversed, toSpliced, and with (replace one index). findLast/findLastIndex search from the end. These remove a whole class of "oops, I mutated it" bugs that plagued sort and reverse.

Power-ups you unlock

toSorted/toReversed/toSpliced return copies
with(i, v) replaces one index immutably
findLast / findLastIndex search from the end
Removes accidental-mutation bugs

The Mutator attacks — common mistakes

Still using sort/reverse where copies are safer
Confusing with() (immutable) with splice (mutating)
Assuming old browsers have these

Boss battleSort an array immutably with toSorted and prove the original is unchanged.

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 orig=[3,1,2];const sorted=orig.toSorted((a,b)=>a-b);
document.getElementById('o').textContent='orig='+orig+'\nsorted='+sorted;</script></body></html>

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