Q: How do you flatten a nested array recursively in JavaScript?

function flatten(arr) { return arr.reduce((acc, item) => acc.concat(Array.isArray(item) ? flatten(item) : item), []); }. If an item is an array, recurse. Otherwise, concatenate.

Question 1

How do you reverse a string recursively in JavaScript?

Accepted Answer

function reverse(str) { if (str.length <= 1) return str; return reverse(str.slice(1)) + str[0]; }. Take the first character, reverse the rest, and append the first character at the end.

Question 2

How do you flatten a nested array recursively in JavaScript?

Accepted Answer

function flatten(arr) { return arr.reduce((acc, item) => acc.concat(Array.isArray(item) ? flatten(item) : item), []); }. If an item is an array, recurse. Otherwise, concatenate.

Question 3

How do you traverse a tree recursively in JavaScript?

Accepted Answer

function traverse(node, callback) { callback(node); if (node.children) node.children.forEach(child => traverse(child, callback)); }. Call the callback on the current node, then recurse into each child.

Question 4

How do you calculate factorial recursively in JavaScript?

Accepted Answer

function factorial(n) { if (n <= 1) return 1; return n * factorial(n - 1); }. Base case: 1 returns 1. Recursive case: n * factorial(n-1).

How do you reverse a string recursively in JavaScript?

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