Problem Statement
Which is not a built-in array iteration form in TS/JS?
Explanation
`for…in` exists but is not ideal for arrays—it iterates enumerable keys (including custom properties) as strings. Prefer `for`, `for…of`, or `Array.prototype.forEach` for arrays.
Code Solution
SolutionRead Only
const arr = [10, 20, 30];
for (const v of arr) {/* values */}
arr.forEach(v => {/* values */});
for (let i = 0; i < arr.length; i++) {/* indices */}
// for...in iterates keys as strings; avoid for numeric arrays