Closure CavesISSUE #11 of 61

arguments · the legacy array-like

LambdaVSThe Mutator

Lambda saysThe arguments object is an array-like list of all args in a regular function (legacy; prefer rest).

Inside a non-arrow function, arguments holds every passed value, even unnamed ones. It's array-like (has length/indexing) but not a real array, so methods like map don't work without converting. Modern code uses a rest parameter (...args) instead — it's a real array and clearer.

Power-ups you unlock

arguments = all args in a regular function
Array-like, not a real array
Arrow functions have no arguments
Prefer rest parameters (...args) today

The Mutator attacks — common mistakes

Calling array methods directly on arguments
Expecting arguments inside an arrow function
Using arguments where rest is clearer

Boss battleSum all arguments via the arguments object, then rewrite with a rest parameter.

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>function sum(){ return [...arguments].reduce((a,b)=>a+b,0); }
document.getElementById('o').textContent='sum = '+sum(1,2,3,4,5);</script></body></html>

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