Array.from({ length: n }, fn) is the cleanest way to produce a fixed-length array. The first argument is an array-like with a length, the second is a mapping function called once per slot with (value, index). Use it for random fillers, index-based sequences (i => i * i), or any computed default. For a constant value, new Array(n).fill(value) is shorter, but be careful: passing an OBJECT to fill shares the same reference across every slot, so new Array(3).fill({})[0] === new Array(3).fill({})[1] is true for the same call. Use Array.from({ length: n }, () => ({})) to get fresh objects per slot.

Rest parameters (...args) are the modern way to collect call arguments into a real array; arguments (the legacy object) is array-like, not an array, and arrow functions do not even bind it. Use rest parameters in any new code so you get .map, .filter, etc. for free. Array.of(...) is a small but useful sibling of Array.from: it always treats every argument as a value, so Array.of(3) is [3], while new Array(3) is a sparse length-3 array. Reach for Array.of when you might pass a single number and want it as a value rather than as a length.

Returning a function from a function is the simplest form of currying and the everyday shape of higher-order programming in JavaScript. addN(10) does no work itself; it returns an array transformer that adds 10 to each item. The transformers compose: feed one's output into the next, or wrap them in a pipe helper that walks them left-to-right. This pattern is the same one Lodash uses for _.curry and Ramda uses pervasively, and it keeps array transformations declarative without giving up the standard .map/.filter/.reduce toolkit.