Transformations

Sometimes we want to transform an array into a new array or another kind of value. We can use:

• slice
• concat
• filter
• map
• flat
• reduce
• join

When we copy elements from the original array to a new array, we're only copying references. In other words, mutating an element in the copy will mutate it in the original array too. We often call this a "shallow" copy.

Slices

We use slice to create a copy of part (or all) of an array.

Concat

We use concat to join multiple arrays in a new array (as an alternative to the spread syntax).

Any parameters that are arrays are flattened into the new array. Any parameters that aren't arrays are added as elements directly.

Spread is usually more concise than concat, and therefore more common in code.

Filter

We use filter to make a new array that contains a subset of the elements of the original.

Map

We use map to transform each element into a different element (potentially of a different type).

Flat

We use flat to flatten nested arrays into a single array. There's an optional depth argument to flatten recursively.

Reduce

We use reduce to combine each element in the array into a single value (of an arbitrary type).

Join

We use join to combine each element in the array into a single string, seperated by a separator string argument.

Each element is first automatically converted to a string with toString