Array Map and Filter

map returns a new array by transforming each item. filter keeps items that pass a test. reduce folds a list into one value.

• map keeps the same length.
• filter returns a subset.
• join turns an array into a printable string.

const nums = [1, 2, 3, 4];
const doubled = nums.map((n) => n * 2);
console.log(doubled.join(", "));

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