The normalize() method of String values returns the Unicode Normalization Form of this string.

The flatMap() method of Array instances returns a new array formed by applying a given callback function to each element of the array, and then flattening the result by one level. It is identical to a map() followed by a flat() of depth 1 (arr.map(...args).flat()), but slightly more efficient than calling those two methods separately.

The filter() method of Array instances creates a shallow copy of a portion of a given array, filtered down to just the elements from the given array that pass the test implemented by the provided function.

The Promise[Symbol.species] static accessor property returns the constructor used to construct return values from promise methods.

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The Map.groupBy() static method groups the elements of a given iterable using the values returned by a provided callback function. The final returned Map uses the unique values from the test function as keys, which can be used to get the array of elements in each group.

The concat() method of Array instances is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

The copyWithin() method of Array instances shallow copies part of this array to another location in the same array and returns this array without modifying its length.